All thread passes through the supports(former slides?).
Knob with threaded center(and a through hole) at the far end.
The all thread does not rotate(not intentionally).
The fingers need some support the keep them from twisting etc.(attach to a wood slide that bears against the 'floor' of the jig?).
Key to accuracy will be to ALWAYS adjust from the same direction*, and a lock(another jam nut/knob?).
*I leave it as an 'exercise' to ponder which 'direction' is better!:D
Also thrust washers where appropriate.
