Apparently there are two versions - one with the "headless" bolt like you pictured - retained by a set screw from side of knuckle - and another where that bolt has a hex socket on the end and bolts through the front of the knuckle.
The part I need is the version of the bolt with the hex end. Alternately I do have one of the bolts as you pictured - so I could swap the knuckle with one that has the set screw port in the side instead of the bolt hole in the front.
If after reading all this you want to swap a knuckle or a "hex version" of the bolt for a collar we can make that happen.
Thanks!