Wheel sensors

[The Gecko_imp]

with an inside caliper. measure w this (or similar), then measure the tips of the caliper with your hand held digital caliper, or micrometer. Id bet harbor freight has these. Ive had mine forever from way back. make sure you get a small pair, obviously.

Thanks for your input, Mike in South Carolina (??)
The problem is access to the sensors and casing, a gauge like this cannot get where it needs to go. I am sure there is a way to measure, similar to what you show, but I don't know of any in the sub millimeter range.