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Hex head or some head bolts for trunking
Baldyhugh 11001211038
57 Posts

Im currently nearing completion of a steel trunking job and was looking for some advice. The 3x3 steel trunking is fixed on top of unistrut running perpendicular to it at regular intervals. I used M10 zebedees and hex head bolts for this. I now wondered if I should have used dome head bolts instead for the same reason as M6 dome head bolts are used to bolt the trunking together - to protect the cable. Was just wondering what others use in this circumstance

5 Replies
OMS 615869
646 Posts
M10 Hex heads holding trunking down on Unistrut is perhaps a bit of overkill

More traditionally would be M6 Slotted Dome heads (ie gutter bolts)

Assuming you don't need a lump hammer to put the lid on, and you take a bit of care when installing cabling, I wouldn't have any reservations about hex heads showing inside the trunking



Baldyhugh 11001211038
57 Posts
Thanks OMS

Thankfully there aren’t many circuits in the trunking however who knows what may be added over time. I think I’ve found some M10 dome head bolts that tighten with an Allen key after a bit of googling so for peace of mind I might replace the hex head bolts with these

Thanks for your reply

Blencathra 11001209918
67 Posts
You could always get some plastic covers for them, blob of superglue must be easier than swapping them
mapj1 80733779
2070 Posts
is it actually going to vibrate and fret the insulation? - if it is part of some big machine, perhaps, but in a building, I'd not think so.
Baldyhugh 11001211038
57 Posts

thanks all for your replies. On another note, what fixings do others use when fixing trunking for example to a surface? Countersunk or panhead screws? Different contractors I have worked with have used both. I must admit on larger steel trunking, a single red rawlplug and screw every couple of feet doesn’t fill me with much confidence especially if the trunking could be eventually filled with cables, it’s quite a weight. On this job I used frame fixings and a large flat washer. Some call them concrete screws, they screw into a predrilled hole with no plug required, kind of like a thunderbolt. They have a countersunk head with a torx fitting to drive them in. I must say they did a good job. Do others prefer panhead or countersunk screws for this application

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