During my few months of proper big company training school instruction, I seem to remember being told to go three clicks. Sometimes I do that, and sometimes I don’t. These were regularly calibrated mics, and would, I think, have been set in a temp controlled room to zero at that degree of tension.

70 odd! Why?

The ratchet ensures the tightening “torque” is always the same. So you get repeatable results and if you set the zero point using the ratchet, these results are pretty accurate.

Differences between ratchets and manufacturers do “not influence” accuracy as long as you use the ratchet to zero the micrometer and to take a measurement.

I take my measurements while turning the ratchet and wiggling the micrometer a bit until I get a stable reading and I can not wiggle the micrometer anymore.

Measure a shaft a few times and se how repeatable the measurements are. In general I get within 0.01 mm, (0.0005″) pretty easy.

I also always use the ratchets and get good repeatability. Assuming the mechanics is well built and kept it shouldn’t matter.

Having more than 70 sounds like quite the collection. If the ratchet or friction thimble are operating as they should, the correct operator technique is being used, and the micrometer properly checked and calibrated. It would have to be something really incorrect to ever be as much as .001″ out since the micrometer frame would be slightly bending at that closing pressure, or the anvils not correctly seating against the part surface. If the micrometer is still accurate enough, a few 10ths variation at most would be more like what you should be seeing. Micrometers and especially used one’s are also an assembly of multiple working parts including those ratchet and friction thimbles. There not immune from requiring cleaning, basic maintenance and light re-lubrication after long periods of use.

Mitutoyo in one of their videos recommends using the same number of clicks on a ratchet thimble, but no actual number is given. They also mention that the speed of rotation during those clicks is also important once your getting into the .0001″ range of measurement. I use 3 clicks and rotate just slow enough that I can definitely feel each of those clicks happening while aligning the anvils to the part surface. Until I bought my gauge blocks, I thought I was always getting pretty decent measurement accuracy.When I started actually checking myself against those blocks, I’ve seen very slight but random size differences if I’m not using the same technique and consistency during each measurement. I don’t know about other brands and I’ve no way of accurately measuring the torque. But I’d say there’s no noticeable difference between the torque on any of the Mitutoyo ratchet thimbles I’ve used on their outside, depth and two pin hole mikes. Why there would be large differences between brands seems odd. Logically one would think the manufacturers would pick a light spring pressure that closely approximates what an experienced person would use when making the same measurement by feel.

If anything, my technique and if I’m not being careful has more inaccuracy than any of my measurement tools would. Quite obviously there’s no requirement to even use the ratchet or friction thimble, it’s well proven that using feel can be just as accurate. But it takes steady practice to develop that to the point that it will be the same for every measurement. And I don’t think that feel and what the light drag on the part is supposed to be is something that can be taught or learned in a few minutes. While I can do it by feel, I don’t make dozens or hundreds of measurements like that every day, so I will usually use the ratchets on my measurement tools. Although I don’t when measuring telescoping gauges, for those I do use feel, and I’ll usually take 3-5 hole and gauge measurements just to be confident my measurements come up with a repeatable number I can trust.