I do not know why these are called “screwless” because clearly there is a screw that pulls the jaws together. I believe that this is a good design because the angled screw pulls the held object down flat onto the vise base.
In the foreground here is Sherline’s 2 inch wide milling vise, weighing almost 1 pound. Behind is a 3 inch wide vise from Little Machine Shop, weighing almost 12 pounds.
I was motivated to write this post because I just finished making a new part for the LMS vise, the “nut”.
The original nut, in the foreground, is a bad design. It too easily rotates when you are adjusting the vise jaws and it has too little engagement with the clamping screw. You invest some time in aligning a vise when you clamp it to a mill table, and this time is wasted when you lose control of the nut. The new nut, which is made of some Duronze that was on hand, has much bigger flats so it cannot rotate while the vise is adjusted, and the engagement with the screw is 1/2 inch more than that of the original nut.
Sherline’s nut is one piece, and has a threaded through hole for long engagement of the screw and nut.
Sherline makes the vise base (and many other parts) by CNC milling of aluminum bar stock. The notches for the nut “pin” were made with a ball end mill, so the “pin” ends had to be rounded.
The seller of the first rotary table that I bought (auction site) was tardy in shipping. So to make amends he also sent a well used vise. I replaced its beat-up steel jaws with new ones of aluminum. Of course, I have since used this old vise to the near exclusion of the new one that I had bought with the mill.
Note the step in the vise jaws. This is quite convenient for holding many small objects.