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I'm using 2x4 timber cleats to support the treads for a set of stairs going up to a deck. The stringers are 2x10 and both the stringers and 2x4 are pressure treated pine. What would be the best size and type of fastener to use? I was planning on using M10 carriage/coach bolts.

2 Answers 2

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You're supposed to figure that out from the load table mumbo jumbo.

TABLE 9.14 LAG SCREW (BOLT) CAPACITY FOR SINGLE SHEAR CONNECTIONS (LBS.), page 69, Chicago deck code, PDF.

3/8ths (M10) is the middle of the road; it's better than using 1/4" or 5/16". Use stainless steel fasteners. You must pre drill your holes for cleats. Ideally it's an actually cut stringer; notice how cleats aren't even an option.

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  • Seems like I have 2 options: coach bolts or structural screws. I would think that coach bolts would be the better option.
    – user82609
    Feb 10, 2020 at 22:04
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This article states the usual method is to use four #8 x 3" screws - I am going from memory but I believe that's what I have used in the past. That's quite a bit smaller than what you're planning.

More recently, I have used the angle brackets made by Simpson Strong Tie and others which are made for the purpose.

Simpson Strong-Tie TA

I prefer the way these look and there won't be a question on inspection. The cost isn't a big deal if it is just a few steps. If there are a lot of steps it adds up. There is no doubt the cleats are strong, as long as the wood remains solid.

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  • Yes, the brackets would be better but they're not available where I am. A #8 screw is only .164". That seems a bit on the small side to me.
    – user82609
    Feb 12, 2020 at 20:52

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