This is a design I made from scratch a few years ago. I’m just sharing the idea here, the files are on one of several old SSDs in a container I don’t care to find. (more pics below) This works backwards to how you may first expect, lefty tighty || righty lucy.

The locknuts in the knob get jammed together and held in hex recesses. These nuts are only used to hold the screw securely by the threaded end. There is a nut embedded into the cylindrical spacer that is tightened against the tapered head of the flathead screw to expand the wedge in the miter slot. The cylindrical spacer looking part is locked into position by two slot protrusions that are part of the print, and fit into the channel of the feather board tool. When the knob is turned left, the screw and the cylindrical spacer’s internal nut are tightening together, and expand the slot wedge.

I tried many nut-type combinations, but double locknuts jammed together along with a spline indexed top cap with hex locking recess is the only combination I feel truly confident to use around a tablesaw where my digits are at risk. In the pic with my hand I’m pulling up white knuckle hard and it is nowhere near budging. Up would be its weakest orientation too, it is even stronger in line with the slot channel. This is not a Tee slot either, just a 3 sided simple 3/4in slot.