I went thru this idea over on the HSM forum way back in March 2009.
Never having used One I wanted to know what locked it after you had set it with the button and was told you wind the locking nut up ??? WTF, if you have to wind the locking nut up you might as well wind the stop up ??
Plus what happens when the button disappears round the back.
Pic that someone posted at the time.
So I came up with a single stop arrangement that locked in any position and didn't need a locking ring.
Right imagine the setup the Bridgy has at the moment, one nut and a locking ring, both threaded 1/2 x 20.
Now replace the nut with a shallower 'nut' but has a clearance hole, attached to this by two pins / screws / rivets is a knurled locking ring again with clearance hole.
This locking ring is actually top hatted internally as is actually a cam ring. Inside this cam ring are two half nuts, a lot like bob weights in a dizzy, it is these that are threaded 1/2" x 20.
To operate you open the cam ring, springs, not shown, force the half nuts apart and the whole assembly can move freely up and down the quill rod.
When in position you turn the cm ring to engage the rod, fine tune to position then nip the cam ring to lock.
Two pics to show the section thru the cam ring.
Make sense ??
Never got round to building this and the old POS Bridgy is long gone and I have the same machine as Spurry.
Might ? just gee me up to doing something about it.