Question for the metallic hive minds

Off Topic Maker Matters
#1

I am looking for an flange coupler with set screw that fits a 5/16" square bar. I have searched every description I can think of and cannot find it. Looking for something like this except it is for a square shaft:

Flange collar with set screw

So far, the closest I have come would be to use a flange for a 12mm round shaft and hope the set screws will keep it in place. Surely such a thing for square bar stock exists, doesn’t it?

Thanks in advance!

#2

Have you considered roaching a square hole out of the round hole if you can’t find what your looking for?

#3

Hoping I will need these in volume and would like to avoid that, but …

#4

There are architectural castings available.

#5

Got a link to one or a name to search for?