What is a hammer fixing, and where should I not use one?

Hammer fixings — sometimes called nail plugs or nail-in anchors — exist because a tradesperson fixing forty metres of batten does not want to drive four hundred screws. They trade adjustability and capacity for speed, which is an excellent trade in the right job and a poor one elsewhere.

Step by step

1. Understand how it differs from a plug and screw.The pin has a shallow helical thread rather than a proper screw thread. Driving it home expands the plug in one motion. It is not designed to be tightened progressively, and there is no clamping stage.
2. Drill the hole to the fixing's stated diameter and full depth.The whole fixing goes into the hole, so the hole has to accept its full length plus clearance. A shallow hole means a fixing standing proud that you cannot then drive home.
3. Push it through the item and into the hole before hammering.The plug body should be fully home and the collar against the item, with only the pin head standing proud. Then drive the pin.
4. Drive the pin fully in one continuous set of blows.Hesitant tapping tends to expand the plug in the wrong place. Firm, straight blows in line with the fixing.
5. Use them for what they are good at.Timber battens on masonry, conduit and trunking saddles, cable clips, mesh, insulation board, light brackets, damp-proof membrane battens. Anywhere you are making many identical light fixings in sound brick or concrete.
6. Do not use them where load matters.Shelf brackets, TV brackets, radiators, gates, handrails, anything cantilevered. The capacity is modest and there is no way to verify or re-tighten it.
7. Do not use them in weak or hollow substrates.Aerated block, soft old brick, perforated brick, hollow block and plasterboard all fail under the expansion. Hammer fixings need sound solid material.
8. Do not use them where you will want to take it apart.Removing one usually means drilling the pin out or levering the whole fixing, and that wrecks the surface. If the item is temporary or serviceable, use a screw.
9. Know the screw-drive variant exists.Many hammer fixings have a Pozidriv or Torx slot in the pin head so they can be unscrewed. It is worth buying that version by default — it costs no more and it turns a permanent fixing into a removable one.

Tips

• For a run of battens, a hammer fixing every 400 to 600mm is typical, but the spacing that matters is set by what the batten is carrying, not by convention.
• Never use a hammer fixing to fix into a mortar joint on an old lime-mortared wall. There is nothing there for it to expand against.
• If you are fixing insulation board, use the purpose-made insulation fixings with wide plastic washers instead — a hammer fixing crushes straight through the board.

Common mistakes

• Using hammer fixings for a shelf or a bracket — The capacity is low, the installation cannot be checked by feel, and there is no way to re-tighten. A bracket wants a screw in a plug or an anchor sized for the load.
• Hammering one home when the hole is too shallow — The plug expands against the item rather than inside the wall, so the fixing is loose from the moment it is installed and the item is being held by nothing.