DIYUK Heavy Duty Metal Cavity Wall Fixings & Molly Bolts for Plasterboard & Drywall, Zinc Plated Steel Anchors, M4-M6, 7 Sizes

Heavy-duty metal hollow-wall anchors (often known as molly bolts, hollow wall fixings, cavity wall fixings or heavy duty plasterboard fixings) for fixing into plasterboard, drywall and other hollow-backed panel materials. Unlike a simple plastic push-in wall plug, which only grips the sides of the drilled hole by friction, this is a genuine mechanical-expansion fixing: a slotted steel sleeve that permanently flares open behind the board when the central screw is tightened, spreading the clamping load across a wide area on the concealed face rather than relying on the board material alone to hold a screw thread.

Made from carbon steel and finished with a white zinc-plated coating for general corrosion resistance, each anchor is supplied with its own removable machine screw, so a fixture can be taken down and re-hung without the anchor itself dropping into the wall cavity. Stocked in three thread sizes – M4, M5 and M6 – across seven length options, the range covers everything from lightweight brackets through to genuinely heavy items such as radiators and wall-mounted cabinets.

How it works: the anchor is pushed, or gently tapped, through a pre-drilled hole until its flanged head sits flush against the front face of the board. As the central screw is turned, an internal threaded insert is drawn back towards the flange, forcing the slotted body of the sleeve to buckle outward into a set of splayed “legs” behind the board. This is what gives a molly-bolt-style hollow wall anchor its pull-out resistance over a plain plastic plug – once set, the sleeve cannot be pulled back out through the hole, and it bears against the reverse of the board rather than just the sides of the drilled hole. Pointed spikes on the underside of the flange also bite into the front face of the board as the screw is driven, stopping the whole anchor from spinning in the hole during installation.

Key Features

• Genuine mechanical-expansion anchor: a slotted steel sleeve flares open behind the board when set, unlike a friction-fit plastic plug.
• Wide load-spreading footprint: the expanded sleeve legs bear against the back of the board over a wide area, reducing point-loading and pull-through.
• Anti-rotation flange spikes: pointed spikes on the underside of the flange grip the front face of the board, stopping the anchor spinning as the screw is driven.
• Removable, reusable fixing screw: the captive-thread design lets the screw be taken out and refitted repeatedly without the anchor dropping into the cavity.
• Corrosion-resistant finish: carbon steel construction with a white zinc-plated coating for everyday durability.
• Easy to fit: no specialised tools required.
• Long lifespan: made from durable materials.
• Three thread sizes, seven lengths: M4, M5 and M6, each available in multiple lengths, to suit different board thicknesses and fixture weights.

Specification

Sleeve diameter (D) is the same for every length within a thread size (M4/M5/M6), and the hole must let the sleeve pass through. Sleeve length (L) is measured from the underside of the flange to the end of the sleeve; overall length (l) includes the screw. Always check your fixture’s own fixing-hole size and your board thickness against the anchor’s length before drilling, and keep the drill square to the board face so the anchor can seat and expand evenly.

Material and finish: manufactured from carbon steel for strength, and made to the manufacturer’s own factory dimensional standard rather than a published DIN/EN/ISO fastener number – hollow-wall anchors of this general “molly bolt” type are a widely-used hardware category rather than a single internationally standardised part, so exact dimensions can vary slightly between manufacturers even at the same nominal thread size. The white zinc-plated coating gives useful everyday corrosion resistance.

Fitting overview:

1. Mark and drill a hole through the board wide enough for the sleeve to pass through (sleeve diameter D in the table above), keeping the drill square to the surface.
2. Push, or gently tap, the anchor into the hole until the flange sits flush against the front face of the board.
3. Tighten the central screw – by hand, with a screwdriver, or with a dedicated setting tool for a faster and more consistent result – until the sleeve is felt to flare and lock against the back of the board. Stop as soon as resistance increases sharply, as this is the point the sleeve has fully set.
4. Remove the screw, position your bracket, fixture or fitting over the now-fixed anchor, and re-insert the screw through it to draw everything up tight.

Because the screw can be freely removed and replaced once the sleeve is set, the same anchor can be reused if a fixture is later swapped, adjusted, or taken down for redecorating.

Typical Applications

• Wall-mounted radiators and towel rails
• TV brackets and wall-mounted media units
• Kitchen and bathroom cabinets, mirror cabinets and shelving
• Handrails, grab rails and stair balustrade fittings
• Curtain poles, blinds and heavier window furniture
• Metal frameworks, railings, barriers and stair fittings
• Pipes, ventilation ducts and other building installations
• Brackets, hangers and other mounting elements on walls and ceilings
• Metal brackets, frameworks and hanging fixtures generally, fitted to plasterboard, drywall, gypsum board, particleboard, plywood or laminate panels

Common Questions

Which size do I need?
Choose the thread size (M4, M5 or M6) to suit your fixture, then check your board thickness against the anchor’s length. Sleeve diameter (D), sleeve length (L) and overall length (l) for all seven sizes are in the table above.

What size hole should I make?
The hole must let the sleeve pass through: sleeve diameter (D) is 6.5mm (0.26in) for M4, 8.8mm (0.35in) for M5 and 10.5mm (0.41in) for M6.

Which boards are they for?
Plasterboard, drywall, gypsum board, particleboard, plywood and laminate panels.

Can I take the fixture down later?
Yes. Once the sleeve is set, the screw can be taken out and refitted, so a fixture can be swapped, adjusted or taken down for redecorating.