For those with vises that rack here is an idea that may help.
1 - Anti-Rack Spacer Stack.jpg
It is a stack of 4 spacers that can make up any thickness from 1/8" to 1-7/8" in steps of 1/8".
It shouldn't be difficult to adapt this for other vise styles.
4 Inch Stack In Use.jpg
It is easiest to lay out the spacers and drill the hole before cutting to dimension.
Half Inch Layout.jpg
When cutting the steps check that the smaller spacers will fit freely in the step before cutting to final dimension.
6- Testing Step Clearance.jpg
I used a 3/8" dowel with a larger dowel glued to the thinest spacer for added strength. The end cap has an interference fit on the dowel without glue.
Dowel & Cap Detail.jpg
To accommodate more sizes a separate 1/16" spacer and a 1"X2" block is also useful.
16 & 1X2 Spacers.jpg
DOH! It is likely most may have figured this out, but I forgot to mention the spacers are 1/8, 1/4, 1/2 & 1" thick.
Also there is a step on the 1" spacer for added strength.
jtk