How deep should a fixing go?

Learn to judge exactly how deep a wall plug and screw need to go so a fixing holds properly and safely.

FD-01Work out what you're drilling intoKnock on the wall with your knuckle. A hollow, drum-like sound usually means plasterboard (a thin plaster-and-paper board wall, often with a cavity behind it). A dull, solid thud means masonry - brick or blockwork, common in older solid walls. This matters because plasterboard and masonry need completely different fixings and depths. The mistake beginners make is assuming every wall is the same and grabbing whatever plug is in the packet.

FD-02Match the wall plug and screw to the wallA wall plug is a small plastic sleeve you push into a drilled hole; the screw threads into it and forces it to grip the sides of the hole. For masonry, use a standard wall plug. For plasterboard, use a proper plasterboard or cavity fixing, since standard plugs won't grip a thin board. Check the packet - it tells you the plug's length and the minimum wall thickness it needs, and your screw should be long enough to pass fully through whatever you're fixing plus the full length of the plug.

1 pack · Wall plugs (assorted pack)

Buy:ScrewfixB&QToolstationAmazon

1 pack · Screws (assorted pack)

Buy:ScrewfixB&QToolstationAmazon

FD-03Check for cables and pipes before you drillRun a cable and pipe detector (a handheld tool that beeps or lights up near hidden wiring or plumbing) over the area first. But treat this as a warning system, not a guarantee - detectors can miss cables that run deep, sit in metal conduit, hide behind metal-backed plasterboard, or simply don't follow the usual safe zones, which is common in older or amateur wiring. Expect something to be there and prove otherwise, rather than trusting a clear reading alone. If you have any doubt at all, isolate the circuit at the consumer unit (fuse box) before drilling, and turn the water off at the stopcock before cutting into anything that could carry water.

FD-04Mark your drill bit for the right depthWrap a small piece of tape around the drill bit at the depth you need - usually the length of the plug plus a couple of millimetres. This gives you a visual stop so you know when to stop drilling. The common beginner mistake is drilling too deep, which risks hitting something behind the wall, or too shallow, so the plug never seats properly and sticks out.

FD-05Drill the hole steadilyFor masonry, use a drill with hammer action switched on and a masonry bit. Let the drill do the work at a steady, moderate speed - don't lean on it hard. Pushing too hard is the classic mistake; it cracks the surface around the hole and doesn't actually drill any faster.

FD-06Push the plug in flushPush the wall plug into the hole by hand, then tap it gently with a small hammer until it sits flush with the wall surface - not sticking out, not sunk below it. If it won't go in, the hole may be slightly too small or too shallow; don't force it, redrill instead.

FD-07Test the fixing before you trust itDrive the screw in and feel for firm, steady resistance the whole way - that's the sign you've got the depth and plug size right. If the screw spins freely without gripping, or the plug spins or pulls out with the screw, the hole is too big, too shallow, or the wrong plug for the wall. Sort this out now, before you hang anything heavy on it.

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