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I am putting in a handrail down the few steps into our garage. The floor is concrete, so I've ordered a couple of 3x3 aluminum posts. The railing has a single attachment point per post, and the hardware that came with it includes lag screws; but I'm thinking those are intended for attaching to wood studs, not aluminum posts. How should I attach the handrail to the posts? I'm thinking a bolt, all the way through the post?

EDIT: I'm mainly interested in the strength of the attachment, as it needs to bear 300lb.

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    Be careful how you set the aluminum handrail in the concrete slab. DO NOT let the aluminum touch the concrete. – Lee Sam Mar 9 at 17:07
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The handrail and brackets you reference will require a through BOLT not a self- tapping screw.

Because it’s 4’ long and stands off the face about 2” (1 1/2” is minimum by Code), the load on each end of handrail will be 300 lbs. / 2 = 150 lbs. at each connection. A 1/4” stainless steel through bolt would suffice for that. (1/4” bolt in double shear will hold 1 - 2 kips, depending on the grade of steel, etc.)

However, more importantly, because the bracket holds the handrail off the face of the post and the bracket does not have much of a resisting “arm” on the bottom of the bracket, the resistance is dependent on the size of the nut/washer, size of hole in post, etc.

If you look at their installation guide, they provide 2 - 5/16” lag wood screws. I doubt you’ll be able to modify the hole size to accept a larger bolt, so using a 5/16” stainless steel through bolt is probably your only option. The “weak link” to your system is going to be the thickness of the wall of your posts (which can be improved by using a larger washing on each side of the post).

Also, if you look closely at the installation instructions for the post, you’ll see it is designed to be screwed down to a wood deck. This will not work for your installation. You’ll need to modify the base and get expansion anchors to secure it to your slab.

  • Gonna go with a stainless bolt all the way through, with a good-sized washer on the back side. Thanks! – Paul Price Mar 13 at 3:59
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If you can find these self tapping metal bits, they will do the trick. enter image description hereenter image description here

They are a lot more robust then they look. I couldn't find the gauge of the post but worse case scenario you could mount a block to the post using two self trappers and go through the railing mount with a third self trapper.

simply google enter image description here from a google search

The list of nobility is quite complicated, it's not meant for the typical tradespersons to understand. A galvanic reaction is used to galvanize a material to prevent it from having a reaction as a result of a large gap in nobility. Materials are galvanized to reduce galvanic reaction. Now get off my back.

also from a google search enter image description here

  • Shouldn’t the fasteners be aluminum? – Lee Sam Mar 9 at 17:02
  • Nope aluminum fasteners have very little strength. – Joe Fala Mar 9 at 17:22
  • Use more fasteners...or find aluminum bolts that are stronger. What about galvanic action? At least you’ll eliminate corrosion. – Lee Sam Mar 9 at 17:35
  • @LeeSam see above. This isn't a forum for arguing. Take it YouTube if you want to argue with someone persistently. – Joe Fala Mar 9 at 17:49
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    If you choose the screw pictured they are available at Brofasco HD supply and they are very strong. I'm 200lbs and I can hang off 1. The part I couldn't figure out was the gauge (thickness) of the post wall. They bite in pretty good. The first time I used them was actually on aluminum fencing, actually supplied by the fence manufacturer. – Joe Fala Mar 10 at 1:00
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Ali fasteners will be very weak - stainless screws are normally used with Aluminium. If the piece of Ali is very large and the stainless screws are very small, then there will be very limited galvanic action.

But what you can do is isolate the metals -Tef gel prevents galvanic action in stainless screws

But really - handrail brackets should really be bolted not screwed.

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