Bolt through or drill and tap?

Is the post solid, or a square tube? Either way, an 8mm hole in a 10mm post doesn't leave much meat either side!

Caveat of "unless it's a decent thickness tube wall."

However, rivnuts are the thing the OP wants.

I guess it isn't *really* a 10 mm square post?

I'd normally agree with you about tapping for neatness at the ends, subject to having enough meat. But a dome headed bolt (carriage bolt) with the dome on the outside should be reasonably inconspicuous. What loads does the bracket see? If seeing fluctuating loads (e.g. wind loads) there is something to be said for the through-bolt because that gives you a better load path.

Not really. Even if it's solid, there's not much each side of the hole.

They are if it's a tube. Don't think they'd work if it's solid. That's why I asked. And I don't think you'd get an M8 rivnut in a 10mm wide tube - you'd have to use a smaller bolt.

Drilling and tapping for a 8mm bolt?, never usually done, but to drill and tap for an 8mm hex head screw, that's better. You would need the correct tapping drill and 2 8mm taps, one starter or taper, and the other a 3rd or finish tap.

But as others have said, bolt through would be my option, but not using an 8mm bolt through a 10mm square bar.

Can you not use wider steel as in 12mm or 16mm is better.

If you think about it a post which is 10mm square is not really substantial enough for a post. 10mm = 3/8 inch approx. 8mm = 5/16 inch approx

Mea culpa. Didn't read the 10mm tube size. 8mm too much in any way shape of form for that size of tube.

Scott

Gah! I blame the keyboard!! There is a '0' missing there.

So thanks for the responses and let's try again :-(

Uck off big brackets to hold 2 * 5 timbers to support some plastic for a car port.

I also expect to hang a pair of hinges off one of the posts, so the same applies - through bolts or tapping for hex head bolt/screw (what is the difference?).

Possibly different answer for the brackets and the hinges.

Cheers

Dave R

There are things available like a bog pop rivet but they are threaded on the inside for just this purpose.

Or weld the fixing on.

I would drill an 8 mm hole on one side and a bigger hole the other for a length of steel tubing to make a spacer. If you don't you may compress the tube and mangle the powder coating.

I go back to the advice of rivnuts! :-)

Also, if you want to bolt through, how about drilling through at 8mm and then opening out the 'other' side to 20-odd mm to let you put the nut inside the post with clearance for the 13mm socket[1]. The 20mm ish hole can then be capped off with some form of cap/gromit.

Scott

In case case, I agree with the person who suggested Rivnuts - see

They will give a firmer fixing than simply tapping a thread in the wall of the tube.

If the tube is, say, 2mm thick, then an M8 thread will give 1.6 threads and that might not be enough to withstand the tension plus other loading.

Takes 3 threads to give full strength or so we apprentices were told.

Pretty sure it is more than 2mm thick - having picked the damn things up.

However advice upstream about the general difficulty has confirmed that we bolt through.

Bought the bolts yesterday - although I didn't think I would have so much trouble finding M10 140mm bolts. Screwfix only do up to 120mm.

Mainly using 150mm M10 and will trim the end afterwards.

Cheers

Dave R

Might depend on the quality of the material, so steel would be OK at that. I've always tried for 1,125 diameters (as I was told) if possible, especially for high torqe applications.

So where did you get them from?

TIA

Wonderful old fashioned firm with lots and lots of interesting nuts, bolts, hinges etc. and not that expensive either.

They only had 4 * M10 140mm, but plenty of 130mm and 150mm.

I made up the numbers with the 150mm and will cut them back when my tuit becomes round.

Also impulse bought some galvanised hinges for the gate I am eventually going to make.

Cheers

Dave R