Eye bolt and plug

The 12 mm eye bolt screwed into a wall plug that gives the scaffold tie its fixed point on the building and carries the full anchor force.

Also called: ring bolt, eye screw, scaffold eye bolt, anchor plug, wall plug

The scaffold tie needs a fixed point on the wall to hook into: the eye bolt, held by a plug in masonry or concrete. It is small, cheap and quick to fit, yet carries the whole anchor force. In a storm these points are what hold the scaffold to the facade.

Design and sizes

The usual scaffold eye bolt is galvanised steel with a diameter of 12 mm. Its head is a closed, welded eye; the other end carries a coarse wood-screw thread that cuts into the plastic plug. Open or merely bent eyes have no place on a scaffold.

Lengths: common sizes run from about 90 to 350 mm. Short bolts for shell work and facing brick, long ones for rendered or insulated walls, so the eye sits just in front of the surface.
Plugs: polyamide expansion plugs, for 12 mm bolts mostly with a 14 mm drill hole and in several lengths. Perforated brick, aerated concrete or high loads call for special or injection anchors.
Cover caps: close the hole after dismantling so no water gets in and the point can be found and reused.

On insulated walls a long bolt alone is often not enough, as its free shank hardly resists shear; special insulation anchors are used.

Fitting step by step

Assess the substrate: concrete and solid structural brickwork hold; render, unbonded facing skins, timber cladding or insulation alone do not.
Drill at the height of the later tie connection, just below deck level at the node. In perforated brick drill without hammer action so the webs do not break.
Blow or brush out the hole – drilling dust costs noticeable holding power.
Insert the plug flush, on rendered walls right into the structural backing.
Screw in the bolt until it is tight with the eye as close to the surface as possible, then turn the eye upright so the hook drops in cleanly.
Where required, carry out and record pull-out tests, then hook in and clamp the tie.

Pull-out tests

If capacity is not documented by approval or calculation, it is tested on site with a pull-out tester. The proof load and the share of anchors to test follow the system instructions and the rules in your country – masonry generally needs more tests than concrete. A competent person selects the points, and the results are kept for as long as the scaffold stands. In the UK, NASC guidance covers tie testing.

What to watch

Old plugs: reuse one left in the wall only if firm and undamaged, otherwise drill beside it.
Edge distance: keep clear of reveals, joints and corners, where brick breaks out.
Wrong fixing points: downpipe brackets, window frames and railings are off limits.
Bent eyes: reject, however new the bolt looks.
Used or new: eye bolts can be reused if thread, eye and weld are perfect. Plugs and caps are consumables and bought new.

Eye bolts and plugs are listed with the wall ties; see also the anchoring guide.

Frequently asked questions

Which plug fits a 12 mm scaffold eye bolt?

Usually a plastic expansion plug for 12 mm bolts with a 14 mm drill hole. Plug length depends on the wall build-up and render thickness; perforated brick or aerated concrete need special anchors.

How deep must an eye bolt go into the wall?

Deep enough that plug and thread sit fully in the load-bearing backing, not just in render or insulation. The eye should still be as close to the surface as possible.

What happens to the holes after the scaffold is struck?

The bolts are unscrewed, the plugs usually stay in the wall and are closed with cover caps. That keeps water out and lets the points be found and, after checking, reused.