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I am fitting some new joists in my roof and will be bolting the new joists to the existing rafters. Both joists and rafters are 47mm thick.

After some advice from a friend (which may of course be incorrect!) I plan on using M12 x 110 hex bolts and timber connectors in-between:

BoltTimber connector

My problem is I am unsure which combination of nut & washer to use. Some possibilities:

  • split ring washer with standard hex nut

Split ring washerHex nut

  • flat washer with nyloc nut

Flat washerNyloc nut

Which is best?

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The spikey washer needs to go between pieces of wood. I doubt its usefulness, since the strength is either going to come from the bolt in shear, or friction between the wood surfaces, depending on how tightly it's bolted. The teeth won't fix poor clamping.

A lockwasher needs a lot of compression to function properly, it's really intended for metal. If backing off is a concern, use the nylok or a second "jam" nut.

You'll want large metal washers against the wood on both ends, otherwise the bolt heads will just sink into the wood when you try to torque it down.

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  • Yes, the spike is for inbetween. I included it because I read somewhere (can't remember exactly where, I've been doing a LOT of googling!) that you should always use one for timber/timber joins. That does confirm what I was thinking about the lock washer. So, the washer I have pictured above is too small then? Something like a fender/penny washer would be more appropriate?
    – Shevek
    Jun 8 '16 at 0:08
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    Yeah, I'd use a fender washer, a fender washer undre a normal washer to spread force, or bigger if you can homebrew it. Another method popular in the US is Simpson Strong-Tie, google it, maybe your country has something equivalent for your dimensions of lumber.
    – Harper - Reinstate Monica
    Jun 8 '16 at 1:53
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    I found some 50mm square washers. A google for Simpson Strong-Tie revealed a brand rather than a product...?
    – Shevek
    Jun 8 '16 at 6:29
  • Yeah, they make a whole mess of products, steel brackets for binding wood structures together in any way imaginable. When I go down to the local galvanizing shop, they have truckloads of them all over the place.
    – Harper - Reinstate Monica
    Jun 8 '16 at 21:30

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