The ball attachments are hardened steel balls with .200” and .250” diameters which are placed on the .250” and .315” diameter anvils, respectively, by rubber caps.
With these attachments, regular micrometers can measure cylindrical wall thickness, but, .200” or .250” must be subtracted from the readings.
Other attachments shown here are either .500” or 10mm in length.
The added amount must be subtracted from the reading.