Lesson 4/Learning Event
a. Center gages, Figure 51, Part A, are graduated in fourteenth,
twentieth, twenty-fourth, and thirtieth of an inch. The back of the
center gage has a table giving the double depth of thread in
thousandths of an inch for each pitch. This information helps you
determine the size of tap drills. Sixty-degree angles in the shape
of the gage are used for checking Unified and American threads or US
standard threads and for checking thread cutting tools.
b. Screw pitch gages, Figure 51, Part B, are made for checking the
pitch of US standard, metric, national form, V-form, and whitworth
These gages come grouped in a case or handle, like
thickness gages. The number of threads per inch is stamped on each
blade. Some types have blade locks. The triangular shaped gage has
51 blades covering a very wide range of pitches, including 11 1/2
and 27 threads per inch for V-form threads.
CENTER AND SCREW PITCH GAGES (PARTS A AND B)