No. 29 – Screw Thread Micrometer Caliper
Image From Catalog No. 18
This caliper will not measure the actual diameter of a V-thread screw, but for purposes of comparison it has a wide range of uses. It is valuable for making a tap the same diameter as some other tap or screw, or a few thousandths larger or smaller.
For cutting screw threads in the lathe to fit nuts, the tap may be measured and then the threads readily cut to same size and to fit nuts, without the common cut-and-try method and its consequent loss of time.
The terminals are not made to a sharp point, but instead are flatted to about 1/64″ inch diameter, and the tool is adjusted to 0 when these flat points are in contact, so it may be used same as any other micrometer when it is desired to measure at the bottom of a groove or a small recess, the thickness in the center of twist drills, or similar work.
Image From Catalog No. 18
Pictures of various No. 29 examples:
All Images courtesy of the J.T. Slocomb Archive
