As Jeff mentioned the hook would have to be sweat soldered on to a 410 barrel - the wall of the 410 barrel would probably be to thin for a dovetail. which is why it used the odd mount. Numrich has the parts for the bracket but do not have the screws, for this mount your barrel needs a small round cut for the cross screw, I assume it must have one, mine has two, possible for slightly different length forearms.

.gunpartscorp/1041940
gunpartscorp/1041930

The large screw is a standard 5/16" thread with a shank just over 1 3/8" with a rounded end where it contacts the front of the forearm and looks like it has almost the same head size a standard Allen head bolt. The original screws have diamond knurling and most hex head cap screw are straight knurled so it would look almost original if you plugged the hex socket.

The small screw is a #5-40 and are available from Brownell's in 1" lengths, full threaded.

I have/had an extra complete bracket but I cannot find it at this time.... evidently my bracket must also have had a set of legs...

Pictures are form an older cell phone, very poor quality.
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