Usually with reamers, their size is stamped at the base of the reamer just above the end of the taper. However I have had reamers with no specific markings and these I found to made for the aircraft industry where very specific sizes are required not being standard metric or imperial sizes. I have undertaken subcontract work for this industry and frequently had to use such items.

Ken Price

Ideally, you need to find someone with a v-anvil micrometer. The angle of the V needs to be correct for the number of flutes – 60 degrees for 3 flutes, 108 degrees for 5 flutes and 128 degrees 34 minutes for 7 flutes. They are not cheap! An ordinary mike will not give a correct diameter.

V-angle mics are also used to detect lobing on centreles-ground spindles.

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Mark,

I suspect that the reason for not adopting your very practical approach is evident from Steve's introductory comment.

MichaelG.