304 (A2) · Class 5
Shear Nut
Break-off security nuts, M6 to M20, in 304 stainless and hot dip galvanised.
About the Shear Nut
Shear nuts are security nuts you tighten with an ordinary spanner until the hex snaps off, leaving a smooth cone that cannot be undone with normal tools, for signs, fences, playgrounds and street furniture. They come in 304 stainless from M6 to M12 and hot dip galvanised class 5 from M8 to M20, in packs of 100. Choose the finish and size above; the guide below covers fitting and how to remove one if you have to.
Also called security nuts, anti theft nuts or break off nuts.
Features
- Tamper-resistant break-off design
- Shears at a preset torque
- Leaves a smooth cone with no grip for removal
- 304 stainless and hot dip galvanised
- Class 5 / A2
- Metric M6-M20
Applications
- Security and anti-theft fixing
- Signs, fences, playgrounds and street furniture
How a shear nut works
A shear nut has two parts: a hex on top and a smooth, tapered cone underneath that carries the thread. You run it on and tighten it on the hex with an ordinary socket or spanner. When the tightening torque reaches the nut's shear range, the hex breaks away, leaving only the smooth cone on the bolt. With no flats left to grip, the nut cannot be undone with normal tools, which deters tampering and theft.
Shear nuts are used for signs, fences, playgrounds, street furniture and other fixings in public places. Pair them with a bolt whose head also gives no grip, such as a cup head bolt, so neither side of the fixing can be turned.
Shear nut sizes
Every shear nut we carry. Select a size to open it in the selector; where both finishes exist it opens the galvanised nut, and you can switch the finish there.
Shear nuts, metric coarse thread, smallest to largest. A blank cell means we do not carry that size in that finish. All sold in packs of 100. Tap a number to show it in the selector above.
How to fit shear nuts
- Fit the job up fully first and check it. Once the hex shears off, the nut is not meant to come undone.
- Use a bolt or threaded rod of the same thread and a matching finish, with a washer under the nut where it bears on timber or a slotted hole.
- Run the nut on by hand, cone end towards the work.
- Tighten on the hex with a socket or ring spanner, steadily, until the hex shears away. For the 304 nuts, drive slowly to avoid galling. Ask us before lubricating the thread: lubricant changes how tight the nut is when the hex breaks off, and Hobson gives no guidance on it for these nuts.
- Check that the cone is seated and nothing is left that a tool can grip.
Removing a shear nut
Hobson publishes no removal method for its shear nuts: they are made to stay on. Treat them as permanent and use them only where the fixing does not need to come apart. If something may need to be removed for maintenance, use security screws or pin Torx barrel nuts instead, which come out with the matching bit.
304 stainless or galvanised: which to use
- Hot dip galvanised (class 5, M8 to M20): a 50 micron zinc coating that Hobson recommends for long term outdoor use. Hobson's corrosion guide lists hot dip galvanising or stainless for anything exposed to the weather, such as fences and open structures.
- 304 stainless (A2, M6 to M12): for a clean finish on signs and fittings. The corrosion guide calls for stainless in the sea spray zone and 316 within 2m of a pool edge; these shear nuts are 304, so near the surf or a pool ask us first. Rust marks on stainless usually come from carbon steel contamination or the wrong grade for the site.
- Stainless threads can gall (lock up) when tightened; Hobson suggests a slower installation speed. Its galling sheet also suggests a thread lubricant, but on a shear nut lubricant changes how tight the nut is when the hex breaks off, so ask us before using one.
- Match the bolt to the nut's finish so one does not corrode before the other.
Shear nuts in Adelaide
Allmat supplies shear nuts, cup head bolts, security screws and washers to councils, sign makers, fencers and trade across Adelaide and South Australia. Add the shear nuts to a quote with the bolts they go on, and we will price the lot.
Shear nuts for signs, fences and public places
304 stainless and galvanised shear nuts, with the bolts and washers they go on, are available to order from Allmat for councils, sign makers, fencers, playground and street furniture installers and trade across Adelaide and South Australia. Order through Allmat, we pick and pack it, then click and collect from the Allmat yard or have it delivered to site.
Goes with
Questions
What is a shear nut?
A security nut with a hex on top of a smooth cone. You tighten it on the hex until the hex breaks away, leaving the cone on the bolt with nothing for a spanner to grip, so the fixing cannot be undone with ordinary tools.
Do I need a special tool to fit shear nuts?
No. Tighten them on the hex with an ordinary socket or spanner until the hex shears off.
At what torque does a shear nut break?
Each nut breaks at its own shear torque. Hobson does not publish it with a unit, so we do not list it: tighten steadily on the hex until it shears off.
Can shear nuts be removed?
They are made not to be. Hobson publishes no removal method, so use them only where the fixing is permanent. For fixings that may need to come apart, use security screws or pin Torx barrel nuts with the matching bit.
What sizes do shear nuts come in?
304 stainless in M6, M8, M10 and M12, and hot dip galvanised class 5 in M8, M10, M12, M16 and M20, all metric coarse thread, in packs of 100.
What are anti theft nuts used for?
Fixings that should not be taken apart: signs, fences, gates, playground equipment, street furniture and other fittings in public places.
Where can I buy shear nuts in Adelaide?
Order through Allmat. Order ahead by phone on 1300 03 03 63 or send your list for a quote, then click and collect from 25 Kapara Road, Gillman, or have them delivered to site.
Shear Nut: sizes and finishes we supply
9 lines by finish. Pick one above for its product code and pack sizes.
| Finish | Sizes | Lines |
|---|---|---|
| Galvanised | M8, M10, M12, M16, M20 | 5 |
| 304 Stainless | M6, M8, M10, M12 | 4 |
Data sheets and documents
The documents for the product you choose are listed with the selector above. Here is every Shear Nut document from Hobson Engineering.
All Shear Nut documents (6)
Data sheets and technical data (2)
Need them in bulk?
Add the sizes you need to your quote, or send us your list and we’ll price the lot and supply it with the rest of your order.
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