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I'm going to be installing a decoupled ceiling into wood joists. The system comprises of clips that each take 4 screws. Each 1.2m x 1.2m 36kg plasterboard will be attached to 12 of these clips total.

Have some SPAX yellox 5.0 x 50mm.

Can't find any info online of shear strength of this specific screw or in general on this type of screw. The screws look pretty tiny for this job, but 5mm is the max diameter of screw that can fit through the metal on the clips. The way the L-shape clips attach to joists is such that the screws will be under sheer load.

Just want to make sure that the clips aren't going to shear off the joists when under load. Thanks for any help.

UPDATE/EDIT: thanks for replies. I'm going to use M5 HEXAGON HEAD COACH SCREW, STAINLESS STEEL A2, and I assume they'll also easily handle the shear load same as the SPAX ones.

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    modern engineered wood screws are crazy strong, these clips are for use by paster board installers so they are intended to be used with regular plasterboard screws or nails
    – Jasen
    Feb 25, 2023 at 12:18
  • Are you sure shear strength is the parameter you care about?
    – SteveSh
    Feb 26, 2023 at 21:53
  • If you're hanging a ceiling from joists, what does shear strength have to do with anything? Are you expecting strong horizontal loads pushing the ceiling panels sideways? Pull-out would be far more important for something hanging over your head, unless it's out in the wind. Also, have you looked at the mfgr specs for your new choice of screws to ensure they're going to meet your need?
    – FreeMan
    Feb 27, 2023 at 17:05

1 Answer 1

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SPAX, on their web site, provides plenty of engineering information about their fasteners. It's not clear which exact product you are using but the "5.0 x 50mm" appears to be closest to their #10 fasteners. The document is here:

SPAX Fastener Engineering Data

The follow chart appears there:

Shear Strength

Note the SHEAR column lists 545 lbs (or 247 kg).

The load you are placing is 36 kg. so even ONE fastener will be able to hold up that amount of weight with a huge margin.

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    Shouldn't OP pay more attention to the Allowable Withdrawal and Head Pull Through values, both of which are way less than the shear and tensile strength values?
    – SteveSh
    Feb 26, 2023 at 19:57
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    Probably but that was not the question.
    – jwh20
    Feb 26, 2023 at 20:29
  • @SteveSh OPs don't always know what they should be paying attention to. I'm guilty of that myself on occasion.
    – FreeMan
    Feb 27, 2023 at 17:03
  • On the other hand there are far too many "purists" who will downvote an answer if it doesn't answer the asked question.
    – jwh20
    Feb 27, 2023 at 17:34

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