I was in need of threaded knobs for MFT with 20mm dog holes. Specifically, I needed a receiver knob for an 8mm bolt that would insure being centered because I was using it for a fence attachment. I decided that it should be a through knob so that it would function regardless of the length of bolt.
I wasn't finding what I was after on here, so I began searching. I remixed some brilliant work by “geo0258” on Thingiverse (linked above.)  His design was simply for the handle and cover that would seat flat to the face. I took his cover, and added a 20mm wide by 21.78 tall base. The setup captures either the bolt head or a nut, so that it can be used as either the male or female attachment.
The setup is designed not to require glue. The hex receiver in the knob capturing the bolt head or nut bears the axial pressure, while the cover threading secures it within the assembly. This not only makes a strong knob, but if you don't torque it down gorilla tight, allows you to disassemble it to change out the nut for a bolt and reassemble it.

This is the only one I've been able to find specifically designed to work with 20mm dog holes. (Not saying there aren't others, but the only one I've come across.) For a lot of people, there won't be a lot of need for this. But for people with an MFT who are used to paying $28-$40 for a set of 4 threaded bench dogs, this can be a game changer.

Feel free to modify as you see fit. But I ask that you, at the very least, give geo0258 the credit for the original base parts, as the creative commons license requires attribution.