Wedge Anchor

How a wedge anchor works

A wedge anchor (Hobson's Clawbolt, also called a stud anchor or expansion bolt) is a pre-assembled, one-piece anchor for solid concrete. You drill a hole the same diameter as the thread, drive the anchor in through the fixture and tighten the nut to a controlled torque. That draws the tapered end up into the expansion clip, forcing the clip out against the side of the hole. It can be loaded straight away.

Uses Hobson lists include handrails and guide rails, formwork supports, mechanical, electrical and pipe brackets, facade installation, stadium seating and racking. Bolting steel base plates, posts and bollards to slabs is a common use too: for any structural or safety-critical fixing, the anchor type, size and embedment come from the engineer or designer's specification, using the ETA or data sheet values.

Clawbolt PRO or standard Clawbolt?

• •Clawbolt PRO carries a European Technical Assessment (ETA). Option 1 (zinc plated, mechanical galvanised and most 316 codes) is assessed for cracked and non-cracked concrete. Hobson's AS 5216 compliance note says anchors with a current ETA comply with AS 5216:2018 when used in line with it.
• •Seismic C1 is for attaching non-structural elements; C2 is the more stringent category, for connections between structural elements. Which PRO codes carry C1, or C1 and C2, is shown size by size in the table below, as Hobson's declarations of performance list them.
• •Clawbolt PRO Option 7 (316, M6 and M8 x 50) is for non-cracked concrete only.
• •Standard Clawbolt (Class 4.6, Class 5.8 and 316) has no ETA, seismic or fire approval. Hobson's Clawbolt data sheet gives its design and working loads in 32 MPa non-cracked concrete, at stated embedment depths and edge distances, for light to medium duty fixings.

Wedge anchor sizes and approvals

A wedge anchor's drill size is its thread size: an M12 anchor goes in a 12mm hole. Length is the overall anchor length in mm; the longer the anchor, the thicker the fixture it can go through at the same embedment.

Installing a Clawbolt wedge anchor

1. Drill a hole the same diameter as the anchor thread, deeper than the embedment you need.
2. Clean the dust out of the hole.
3. Drive the anchor through the fixture into the hole until the washer and nut sit on the fixture.
4. Tighten the nut to the installation torque. Do not overtighten.
5. Keep to the minimum edge distance, spacing and concrete thickness, which are part of the conditions behind every published load.

Clawbolt PRO installation values (ETA-19/0669)

Clawbolt PRO is installed to the values in its own ETA, and which ETA applies depends on the code on the label. Zinc plated and mechanical galvanised Clawbolt PRO codes that do not end in M (for example EAWMSZD18M120120) are declared under ETA-19/0669 (Hobson DoP 10016 and 10017). Drill the hole at the thread diameter to the hole depth, set the anchor and tighten to the torque below with a calibrated torque wrench.

Clawbolt PRO installation values (ETA-25/0105)

Zinc plated and mechanical galvanised Clawbolt PRO codes ending in M (for example EAWMSZD18M120125M), and the 316 codes Hobson declares under DoP 10042 and 10044, come under the newer ETA-25/0105. Its torques differ by finish and its embedments are shallower, so do not mix these values with the table above. In this ETA the minimum spacing only holds with at least a set edge distance, and the minimum edge distance only with at least a set spacing, as shown in brackets.

Which finish for where?

• •Zinc yellow passivate and zinc plated: low corrosion resistance on Hobson's finish comparison, for dry indoor or enclosed fixings.
• •Mechanical galvanised: Hobson rates it high corrosion resistance, similar to hot dip galvanising, and it does not risk hydrogen embrittlement. Hobson's corrosion guide lists hot dip galvanising or stainless as the minimum for exposed fixings in low, medium and high-industrial zones; it does not list mechanical galvanising, so this rests on Hobson rating it similar to hot dip galvanising.
• •316 stainless: for exposed fixings in coastal and seaspray zones, and within 2m of a pool, where Hobson's corrosion guide calls for stainless. 316 is not made to sit in seawater.

Wedge anchor, sleeve anchor or chemical anchor?

• •Wedge anchor: through-fixed in solid concrete and can be loaded straight away; Clawbolt PRO adds ETA approvals. Not for brick or hollow block.
• •Sleeve anchor: also through-fixed in solid concrete, for light to medium duty, with more head styles.
• •Concrete screw: a screw-in anchor that can be removed; its base materials, edge and spacing distances are on the concrete screw page.
• •Chemical anchor: a resin-bonded anchor; the base materials and sleeves it is published for are on the chemical anchor page.

Wedge anchors in Adelaide

Allmat supplies Clawbolt and Clawbolt PRO wedge anchors, sleeve anchors, concrete screws and chemical anchors to builders, steel fabricators, racking installers and trade across Adelaide and South Australia. Add them to a quote with the rest of your list and we will price the lot.

Questions