How to choose crabs for drywall and what they are needed for?

In offices and homes, drywall construction is a common option for smooth, beautiful walls and ceilings. When working with drywall, the "crab," or cross-connector, is a crucial element that guarantees a sturdy and stable structure. These tiny but essential parts are essential for fastening the drywall sheets to the metal frame.

For your drywall project, selecting the appropriate crabs can have a big impact on the installation’s overall durability and quality. Making an informed choice can be aided by knowing the objective and functionality of these connectors, as there are numerous options available. Whether you’re a professional contractor or a do-it-yourself enthusiast, choosing the right crabs will make construction go more smoothly.

The most important factors to take into account when choosing crabs for drywall will be covered in this guide. From comprehending their function to investigating the various kinds accessible, we’ll offer you useful guidance to guarantee your drywall installation is both effective and durable. Now let’s explore the fundamentals of selecting and employing crabs in the process of building drywall.

What it is?

Let us examine not only the notion but also the role of the crab in relation to other methods of fastening metal profiles (MP) of plasterboard frame (sheathing) and related panel assemblies (wall, ceiling, and light partition cladding).

For the sake of brevity, the concept of crabs, crosses, and X-couplings will also be used later in the text to refer to "butterflies" (for a two-level frame); these are the same as those, but with two "claws" instead. We shall refer to both of them by each of the terms listed as well, in the interest of diversity.

There are numerous common sizes for metal profiles (MP) available:

These are the following categories, generally speaking:

• For vertical structures such as partitions, for wall cladding – rack strips (PS) and guides (PN).
• Guide (PN) and ceiling (PP) profiles for ceilings. For this area, crabs are usually always used; here they are irreplaceable, except in exceptional cases of departure from standard rules (we will show it in the photo below).

Citation! Section of plasterboard U-shaped profiles. In other words, there are two shelves and one wall in the structure. The latter are smooth for MP guides and have bends for reinforcement for rack-mount and power ceiling guides.

Sometimes they get confused and refer to MP shelves as walls. This is okay as long as everyone knows what we mean, but it is accurate to refer to the slats’ wide base (bottom) as walls and the sides of the slats as first.

Associated in these ways (we’ll just mention the primary ones):

1. “Cutting with bending” with a special tool called a notch.
2. Extension (overlapping and butt).
3. Connecting slats in the corner of structures.
4. T-joints (by cutting, bending and inserting one end of the rail into the mating strip).
5. X and U-shaped crabs, butterflies. For crossing profiles. our theme.
6. Together with these methods, metal self-tapping screws are usually used (“bugs”, LN – piercing, LB – drilling, TB – self-tapping), in some cases they are mandatory.
7. By inserting into each other and fixing with screws.

To gain a better understanding of the position of X-couplings among them, allow us to present a few more examples of different connectors.

T-shaped connections are used primarily for horizontal slats in a vertical frame between rack profiles (PS) and for the lintels of doorways, niches, hatches, and laying communications. PN strips are used for this purpose.

In two photos, the options below are non-standard and are made assuming that the sheathing is assembled solely from PN:

There are further options for connecting the horizontal frame in a T-shape, such as:

Standard PN (load-bearing) and PP (lintels) profiles are always used for the ceiling, and they are primarily connected in two ways:

• extension (usually using a special insert;
• crabs.

The first technique involves building up slats for all assemblies, not just ceilings. At the intersections of horizontal (suspended) frame slats, cross-shaped couplings are employed.

Although they are not as frequently used, they can be used for the same tasks for any structures, including vertical and other lathing.

Crucial! An element for a metal profile to create a rigid connection at its cross-shaped intersections is the crab found in the plasterboard structure’s frame. Although it can be used for other purposes if needed, its main application is as ceiling cladding. It can also be used for vertical structures like partitions.

There are numerous fastening components, such as different hangers, for ceilings in general (we concentrate on them because this is where you can’t live without a crab):

U-shaped or cross-shaped element; butterfly or X-shaped coupling; crab (shrimp). Branches with tendril-adorned sides are used to latch onto and grasp the profile. created by stamping zinc-coated steel.

Wall Thickness:

As with the profile, the more, the better.

Alternative names:

• cross;
• butterfly;
• shrimp (this name is often used for rectangular, not square, sizes);
• cross or cruciform connector for structural profiles with plasterboard sheathing;
• X-shaped coupling;
• universal connection (connector) crab or just the last word.

There are two kinds of antennae (legs-petals, antennae) on the branches of a single-level X-shaped coupling-connector:

1. Already bent with grips (hooks) on them for snapping onto the profile under its figured recesses, bends on the sides from the inside.
2. Straight with holes for screws. When installing the clamp, they are bent to the outer surface of the sides of the MP and screwed with self-tapping screws, since they have holes for them. They are usually used in any case, but they are especially relevant if the planned load on the sheathing is 20 kg or more per 1 sq. m. .

Take note: The crab’s central axes are equipped with holes that allow it to be fixed to the supporting element either directly or via an adjustable suspension.

The two-level coupling is a suspension-like plate that is bent into the letter P before installation. Its side legs have holes for self-tapping screws, and at their ends are hooks that fit over protrusions on the profile’s sides.

Why are they needed??

At cross-shaped intersections, shrimp are required to connect profiles (crossroads). Because of its horizontal position, other fixation on the indicated segments is highly unreliable, so it is always placed on the lathing for cladding the ceiling.

For increased dependability, the coupling can also be positioned on vertical assemblies; however, these frequently only include vertical posts and do not employ jumpers to form a kind of mesh, making the part less common and less in demand because there may be more reliable alternatives.

The most dependable solution available is to use cross clamps at the joints between the intersecting profiles of the horizontal frames of plasterboard assemblies.

When it comes to ceiling assemblies, couplings are positioned at every intersection. Other connection methods, or combinations of them, are rarely utilized; in this context, crabs are the most practical and dependable option. Each described segment needs to be fixed on vertical frames as well, although in this case, a combination of approaches is already permitted or alternative approaches are typically more practical.

Therefore, the crabs’ job is to join standard guides and racks, perpendicularly positioned profiles, and other frames in a single plane at their intersection. Because they are indispensable and frequently the only option available, these connectors are used primarily for ceiling lathing, though they can be used for any type of assembly.

Note that crab is the best—one could even say the most natural—method for attaching MPs to one another for horizontal battens in terms of stiffness, strength, and dependability.

Additionally, it is simple to assemble and disassemble—just screw or unscrew the screws and snap or unsnap the product—which expedites repairs and the assembly and disassembly of claddings and partitions.

To reiterate, crabs are primarily utilized for horizontal assemblies, like suspended ceilings; other fastening methods are more frequently employed for vertical structures, though occasionally the X-couplings under discussion are also present (see photo 1):

Other approaches, like the one in the picture below, are occasionally used in place of them when it comes to shrimp-specific situations, but these are regarded as unusual and non-standard.

Let’s enumerate the application areas:

• Fastening and rigid fixation (joining) to each other on all possible assemblies sheathed with plasterboard boards (gypsum plasterboard or according to the new marking GSP) and similar materials (gypsum plasterboard, GKP), perpendicularly located, that is, intersecting MP (vertical and horizontal jumpers).
• For ceiling cladding (irreplaceable elements). For connecting slats of suspended structures with a large area and irregular shape.
• When leveling, insulating walls with plasterboard mounted on the sheathing (less often).

Although the crab can theoretically be used for both T-shaped joints and slatted extensions, practical applications for it are rare due to the availability of more dependable techniques, such as bending a cut and utilizing specialty inserts.

Only profiles that intersect are typically connected by a cross-shaped coupling or butterfly connector, and the joining point needs to be in the middle of both.

The connector is attached with self-tapping screws and snaps together with ease using shaped tabs with springy protrusions and/or hooks. The application is simple: in certain situations, metal scissors can be used to change the size (length) of the legs if the model (such as traditional single-level couplings) lacks hooks on the legs.

Varieties

For joining metal profiles of plasterboard frames and related assemblies that cross perpendicularly, there are only two types of X-couplings available by design:

• single-level;
• two-level.

Single-level crabs are made to fix slats that intersect when they are on the same horizontal line without deviating, that is, when they are not above or below one another. And although the element in question resembles a cross, it is actually more of a square or rectangle with its sides cut out to create four leg-like protrusions.

Moreover, the body typically has stripes that stiffen the ribs. To accommodate profiles with varying standard sizes, the product’s legs can have protrusions that vary in width.

Citation. "Butterflies" are another name for two-level cross-shaped connectors for MP structures composed of gypsum plasterboard.

They don’t look like other people at the same level at all. This is a U-shaped, perforated plate that is bent before use, resembling a suspension or fastening bar.

To grasp one and hook the other (lower) from the inside, the width of the body and legs must match the dimensions of the mating profiles. The ends are fixed by the MP folds with semicircular hooks or similar protrusions.

There are screw holes (typically 4–5 pieces) on the sides of the legs, and occasionally they are also on the body. For added comfort, the top is frequently ridged, slotted, and slightly curved to provide spring.

There are choices that lack these characteristics. To ensure a firm grip, the upper portion’s width corresponds to the slats it fastens.

Here, the side and top sections have a slightly different design (this is the Knauf brand; there are other models available):

Two-level coupling has a suspension-like appearance. The element is turned inside out and its legs need to be unscrewed before it can be used. The "butterfly" in its original form is a plate that has not been bent. The images and diagrams we’ve included above and below show how the shape, quantity of self-tapping screw holes, and geometry of the hooks might vary slightly.

However, the element typically appears as follows in the first image:

Take note: Products composed of galvanized steel are the only category of products based on material. Although we have not discovered any on the market, occasionally there is information that there are products made of aluminum alloys.

The choices for wall thickness are numerous:

The first-numbered product is only appropriate for lightweight constructions. An average standard is typically 0.65–0.7. However, it is generally preferable to take 0.9–1.5 mm (the thicker, the better).

Since these products are as standardized as possible, options are available for the width of all types of profiles in terms of standard size. However, 60×27 and 47×17 ceiling profiles (PP) are typically the most popular.

What makes the latter more like a "shrimp" is this detail:

When making your decision, you should review the MP’s specifications and contrast them with the product’s technical documentation. In the documentation, you should find information on whether the MP is appropriate for a particular kind of slat.

On the websites, we could not find crabs for unusual or non-standard profile widths. These choices aren’t often available in casings, though. However, you can still trim and slightly bend the couplings if this plank parameter is out of alignment.

Citation! Companies that uphold their good reputations produce high-quality crabs. Knauf and Gyprok, for instance, may offer products with thin walls (for structures with light loads), but there are also plenty with a parameter of 0.7…1.5 mm.

Furthermore, their zinc coating is typically more dependable and thicker.

Features of choice

The selection process by size was previously discussed; the general rule is as follows: review the profile parameters and contrast them with the information found in the product’s technical documentation. Crabs are typically used for ceilings, and PP 60×27 is frequently the only material used.

Wall thickness is the primary quality parameter. Minimum 0.4 mm, but ideally 0.65…0.7 mm, if the design load is 1 kW. Sheathing should be installed above the designated range (0.8…1.5 mm), ideally exceeding 20 kg.

Additional guidelines for selection:

• The presence of burrs may indicate careless production on low-quality equipment, and deviations from dimensions may also be observed.
• Hangnails do not always indicate a bad product. This is a minor drawback – the product can be cleaned. The main thing is that there are no other disadvantages listed by us.
• Walls too thin.
• Low-grade metal, which can be identified by blackening, rust.
• Rust, corrosion. May arise due to violation of storage standards, due to manufacturing deficiencies.

Crucial! The metal profile’s crab connectors’ shaped legs need to be fastened securely, visibly, and without any backlash or rattling. Petals: strictly bend in a single direction along the slats’ width.

If you select a low-quality product, for instance, even with small size variations, the result will be a significant loosening overall from multiple such unreliable elements.

Not only will the frame bow, but the cladding as well—cracks could show up on it, flaws could show up in the joints, and the cladding itself (the grout will crumble, the reinforcing tape will fall behind). The element should accomplish its goal of joining the MP as tightly and rigidly as possible.

All of your hard work building the sheathing could be in vain if you forget to use shrimp to secure every joint. A "bump" could develop and eventually destroy the entire structure.

Manufacturers and price

Let’s rate popular brands on the market, make some generalizations, and show how much one- and two-level models in the same range cost:

Name	Advantages and disadvantages	Price, rub./PC.), wall thickness 0.9 mm
Knauf	Superior to all brands in all respects. Products are of extremely high quality. Excellent Product Sample. But usually a third/half more expensive.	50…65
Gyproc	Quality like Knauf, but cheaper. We did not find any bad reviews, but traditionally this brand is placed in second place after Knauf, perhaps there are some differences, but they are very insignificant.	40…50
AcousticGyps	The quality is slightly worse, but there are also no special comments. The product is reliable, produced by a highly specialized company.	35…45
STARFIX	Not the best, but acceptable quality at a low price. Sometimes you come across products with burrs. But in general the metal is of high quality, deviations in size are rarely observed.	30…45
Sibrtech, Bilar	Poor quality. There are size deviations. Thin walls, difficult to insert the profile without bending the legs, body. If used with a Knauf MP, the antennae do not fit normally and are deformed.	thirty

Crucial! Our market research revealed that there aren’t many well-known manufacturers that produce drywall crab connectors. There are a lot of small businesses; you can find products of average quality among them, but you have to be picky because the majority make direct consumer goods.

The majority of artisans typically don’t worry too much; instead, they use slightly more expensive Knauf or Gyproc products, which you can trust and save time looking for.

There is not much of a price difference between one and two-level X-couplings for the plasterboard assembly profile. However, the thickness of their walls is the determining factor in all cases; the greater this parameter, the more costly the connector.

Consumables and tools

All you need are self-tapping screws LN or LB with a length of at least 9 mm, and a screwdriver with a Phillips head.

As we’ll cover below, you can also make a metal stand to make screwing in more comfortable.

Fastening rules

As you can see, fix the connectors:

1. Place exactly in the center of the intersection of the profiles. The shape of the shrimp is different and will not allow them to be positioned.
2. Snap the legs with protrusions (two-level models) or, if it is a single-level coupling, position it so that its hooks on the edges of the petals fit into small bends on the sides of the profile. That is, the top itself will tightly grip the other docked MP.
3. Single-level shrimp have bent antennae on the protrusions without holes for screws (for snapping) and those straightened with them. The former should enter the rail cavity. The latter can be left as it is, but in any case it is advisable to bend them on the outer walls of the rail and fixed with “bugs”, it is necessary to make the latter if the load on the crate exceeds 20 kg per 1 sq. m.

Crucial! Use caution when lowering (bending) the crab’s cruciferous connector "paws" for the drywall structure frame. Avoid attaching too much force or pressing too hard in the fold segment to avoid metal breakdown.

Work with connectors

The intricacies of repairing the metal profile shrimp chatter in drywall structures will be examined, accompanied by real-world examples and detailed explanations of the entire procedure using a suspended ceiling example with a GKL (GCP) casing.

We mount one portion of the jumpers (PN) and the perimeter. We push shrimp into the calculated locations where the plan calls for the rest of the profiles to be, or where they will intersect. They slide along the slats with ease.

The cut bars that are positioned perpendicular to the installed ceiling guides are snapped. As can be seen in the picture, the legs that have a protrusion for this reason are located outside the profile cavity, while the legs that have holes for self-tapping screws are bent against the side wall.

Press and snap the outer tab (be sure to lower it and do so slowly and carefully to avoid breaking it at the bend). Tighten the screws to secure the bugs.

Installing crabs with two levels. This type of shrimp is used to attach the lintels to the perimeter guides, as seen in the view of the ceiling below with them fully installed.

Here, it’s crystal clear:

1. The coupling is inserted until it clicks, that is, there should be a feeling that it is inserted tightly, all the way.
2. The hooks on the legs fit onto the protrusions of the sides of the mating (lower) rail.
3. Next, it remains to fasten the bugs on the side folds.

Features and Bugs

The shrimp in the first picture below are positioned incorrectly, with their legs pointing toward the ceiling. This will put additional strain on the product’s landing pad and force the mount to descend significantly. The body’s plane may have been torn apart, leaving it with nothing to rest on.

The connector platform rests on top of the profile in the second picture, which is accurate when the legs are lowered. It is impossible to tear it out in this position, so it won’t be. Furthermore, the coupling protrusions, the planes, are not under any pressure.

The instructions for correctly mounting on an uninstalled rail are provided below. A shrimp with its legs pointing down is pushed between the profile and the ceiling, which has its cavity pressed up against it. You can easily move the crab to any location because it moves as if it’s on a rail.

One, multiple, or all of the legs’ poor or nonexistent latching is another defect. They should enter with a loud click, sit firmly without moving, and allow you to check and adjust the height. We use our fingers to tuck each leg separately in the picture below.

That is, the profile is first fixed to the exact level of the ceiling using dowels (anchors). Next, a crab is pushed between the profile and the ceiling plane, its legs are snapped into position, and it is positioned. Finally, the antennae with holes for the self-tapping screws are bent and screwed in with a screwdriver.

Hardware that is screwed into a solid steel wall frequently jumps off when the legs rise. A clamping bar is formed from a section of the same profile that is grasped from below in the vicinity of the hardware insertion point with one hand, while the other is used to place and screw in a magnetized bit that has a self-tapping screw stuck in it.

Similar features apply to two-level shrimp (installation was covered in the previous section). In this instance, you must ensure that the leg hooks securely fit behind the MP’s side protrusions.

Calculation of X-shaped couplings and butterflies

It is very simple to calculate the number of crabs because it is equal to the number of cross-shaped intersections between the profiles.

• boxes of 10, 100 pcs.;
• in a different package;
• piece by piece.

Crucial! An X-coupling or butterfly fastener must be used at every intersection of profiles. Avoid skipping these areas as there is a chance of loosening, which could harm the cladding and finishing in addition to the frame. Although connectors are not so expensive that you should cut corners, not having them can have a disproportionately negative impact.

As an example, let’s use Knauf circuits. We follow the "KNAUF Complete Systems" instructions for suspended ceilings (executive documentation). Ceilings that are suspended at the element-by-element assembly level (henceforth called the Manual).

One two-level option (the side facing the ceiling plane is depicted):

As we can see, a ceiling profile is used; its inside sides are figured in relief and have curved edges to help secure the hook or allow the crab antennae to snap into place.

LN or LB screws are used to secure the products:

Note: When making single-level (single-axis) frames, the supporting strips are cut and positioned on the first profile after the primary profiles (guides) are fastened to the hangers.

At intersections, a grid is made and shrimp are used. If the ceiling is two levels (two axial), then one rail is positioned above and the other below. In this case, the second rail is completely perpendicular and is not inserted in segments between the guides; in this case, U-shaped butterfly crabs are used.

There is a ceiling profile (PP 60×27) and a guide profile (PN 28×27).

The number of profiles and their pitch must be determined when building a ceiling in accordance with the anticipated load. The Knauf Manual and other comparable documents from other manufacturers, like Gyprok, contain all of these calculations for material consumption. They can serve as samples for any kind of improvised assembly.

An example of calculating crabs per square meter for suspended ceiling schemes using Knauf P112 is shown below.

The layout below indicates that you will require precisely twelve two-level crabs, or twice as many as there are intersections.

All of the calculations are provided in full in the manual as well; here are a few examples:

Crucial! The line for screwing in the screws that hold the plasterboard sheets (also known as gypsum board or, in accordance with the new GSP marking, gypsum board) runs through the joints where the shrimp are found. Hardware TN, MN, and TB are utilized for profiles with walls measuring 0.7 and 0.7…2.2 mm, respectively, for this purpose.

Here are a few of the many diagrams found in the Manual; notice how the plasterboard sheets are fastened to the coupling.

Advantages and disadvantages

For their field of application, X-shaped couplings have no drawbacks.

The benefits include:

• The most reliable connector for criss-crossing headliner profiles, horizontal, suspended assemblies
• The easiest to use – the element just needs to be inserted, snapped, and secured with clips
• It is easy to disassemble the frame in case of repair or dismantling – just unscrew the screws and snap off the product. In this case, the profile is not damaged, and neither is the shrimp – they are suitable for reuse (just do not bend/unbend the antennae often so as not to form a kink)

Selecting the proper drywall crabs is crucial to guaranteeing the longevity and steadiness of your wall or ceiling constructions. In order to provide additional support and stop drywall profiles from sagging or shifting over time, crabs, also known as cross-connectors, are used to join them at intersections. Think about the size and kind of profiles you will be using, the weight of the drywall, and its dimensions when choosing your crabs. Crabs that are installed correctly can help preserve the integrity of your drywall, increasing the dependability and durability of your building project.

Useful video

Take a look at this entertaining video that demonstrates how to correctly attach crabs to the profile:

Aspect	Details
Purpose of Crabs	Crabs are used to connect drywall profiles, ensuring a stable and strong framework for the drywall sheets.
Types of Crabs	Standard crabs and adjustable crabs, each suited for different construction needs.
Material	Typically made from galvanized steel for durability and rust resistance.
Installation	Easy to install by snapping onto profiles, no special tools required.
Choosing Crabs	Consider the thickness of the drywall, the weight it needs to support, and the specific construction requirements.

Selecting the appropriate drywall crabs is crucial to guaranteeing a sturdy and steady construction. These tiny but essential connectors provide a sturdy framework for your drywall by holding the metal profiles together. Your walls might not have the necessary support without the right crabs, which could cause problems later on.

Think about the kind of project you’re working on and the particular specifications of your drywall installation when choosing your crabs. Seek for premium materials that are robust and long-lasting. During construction, you can save time and effort by choosing crabs that are simple to install.

Making an educated choice can also be aided by your knowledge of the various varieties of crabs that are offered for sale. Make sure the single or double crabs you need can support the weight and strain of the drywall while also working with your metal profiles.

Purchasing the appropriate crabs for your drywall project is a minor but essential step that can significantly impact the general caliber and durability of your walls. Making the best connector selections now will guarantee a seamless installation and a reliable, long-lasting outcome.

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