Update!

I received those knobs today, and they are a very poor fit on the Glock stacked pot. There's like 1/16" gap between the shaft and the inside of the knob, so when you tighten down with the grub screw the knobs sit off-center and at an angle, causing them to push against each other at certain points in the rotation. I have temporarily improved the situation by wrapping about four layers of copper shielding tape around each shaft, but in the longer term I will need to get knobs that fit better.
I don't know if the problem with these is a misunderstanding about ID vs. OD, or just really loose tolerances, or if the measurements given in the Warmoth catalog are "nominal" (like a 2x4) rather than "actual", or what.
If anyone has recommendations for a set they know will fit well from real first-hand experience, I'm all ears.