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Pan head or countersunk screws

Baldyhugh
Hi all

Further to a question I posted yesterday regarding using hex head bolts to fix steel trunking to unistrut, some others used dome head gutter bolts instead. These are presumably used so that they potentially damage the cables less than a hex head bolt. Following on from this, what type of screws do others use when fixing steel trunking for example to a block wall. Would you opt for countersunk or panhead screws? Different contractors I have worked with use both and I must admit that on larger steel trunking, the odd red rawlplug occasionally along its length doesn’t fill me with much confidence when the trunking could potentially be full of cable which would be quite a weight. On a recent job with steel trunking I used frame fixings( some call them concrete screws). Basically screws into a predrilled hole in the clockwork and has a countersunk torx head, no rawlplug required.I used these with a large flat washer and it took a great gold but I suppose my question remains are countersunk or panhead screws best (or specified) for fixing trunking or other accessories containing cable?


thanks
  • 0
    Hi Dave


    I suppose the idea being that the rounded head of the gutter bolt offers no sharp edges to potential cable damage but I agree with you that a hex head bolt is in no way sharp and I’d argue that the raised head of a countersunk screw isn’t sharp either. The lip of the steel trunking and the cut and formed edges of the trunking are still sharp regardless of how well they are filed down following cutting
  • 0
    A flat washer with a hole diameter slightly larger than the screw will help reduce the projection of sharpness into the trunking.


    I would think a large hex head bolt is more likely to cause issues than a smaller countersunk screw.


    If the block is soft, the screw may countersink itself to a degree, especially in (i know you didn't ask about this) plastic trunking

    (I do mostly domestic now ...I miss the hell out of industrial).  Are cup washers still a thing? they're typically used for appearance but if you were worried about the abrasion from the sharp edge of a csk screw, they'd be a solution, especially in addition to a regular washer (yes you can get overly fancy) depends on how hard and much cable you're putting into the trunking and are you PUTTING it in or are some sections used as a conduit and the cable pulled through (that'd be a worst case scenario).


    To be fair I'd be happy with csk screws in a penny washer unless i was hauling the cables through. Hex head bolts do have very sharp corners however, domed fasteners would be preferable here, however don't screw up and use them for connecting earths to banjos, finer pitch screws allow more clamping force there :)
  • 0
    well if we are that bothered, and want something that can be driven in by the electric driver then pan head/ button head allen bolts in M6/M8 M10 all exist, and can be pulled up very tight very fast and with a lot less slip slide and risk of cut hands than a flat blade driver. Should have change from the price of a pint for a bag of 50 in steel rising to about 5p each for stainless example

    Do about avoid anything less than about M5 in this head style, the really small ones like M3 tend to  have shallow engagement and can round out too easily - if you must then torx head.

     

  • 0
    mapj1:

    well if we are that bothered, and want something that can be driven in by the electric driver then pan head/ button head allen bolts in M6/M8 M10 all exist, and can be pulled up very tight very fast and with a lot less slip slide and risk of cut hands than a flat blade driver. Should have change from the price of a pint for a bag of 50 in steel rising to about 5p each for stainless example

    Do about avoid anything less than about M5 in this head style, the really small ones like M3 tend to  have shallow engagement and can round out too easily - if you must then torx head.

     



    My first impression was that the OP was describing button head screws, but are we not thinking about what used to be wood screws?


    Problem is that Spax (and others) largely sell countersunk screws and they are what is available in my local builders' merchant. It vexes me to use countersunk screws in back boxes, but they do seem to work.


    As for trunking (or anything similar) the traditional approach would have been round-headed (Japanned) steel screws. The nearest now does seem to be pan headed, so in answer to the OP, that is what should be used.


    As for the driver, my preference (ignoring cost) would be Torx, hex (Allen, not external hex) posi, slot.


  • 0
    I was thinking out loud and overthinking, apologies.... But i stand by the 'hex bolts are more of an issue than countersunk' (simply because they're larger)
  • 0
    well flange head self tappers in 8 gauge go very well into red wall plugs, and being parallel, unlike traditional conical wood screws also work in chip board as well
  • 0
    I must admit that I work with the trade tubs of I think 500 screws and red plugs. The weapon of choice is scrulux square headed screws as this is basically what most of the wholesalers in my area sell. I generally use the countersunk ones being that is what they sell in the tubs and have never really given it a second thought and use them for general day to day fixing of accessories etc and never had a problem. Yes they do sit slightly proud when screwed in but the edge of the screw is not sharp as to cause any cable damage in my opinion. Scrulux obviously do a panhead version which I have also used in the past and a recent conversation with a colleague has made me consider them more and in hindsight may be a better choice for some things in the future
  • Former Community Member
    0 Former Community Member
    LoL - Badgers, Badgers everywhere ?


    OMS

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