Machining Fundamentals
74
4.6.6 Thickness (Feeler) Gage
Thickness gages are pieces or leaves of metal
manufactured to precise thickness, Figure 4-49.
Thickness gages are made of tempered steel and are
usually 1/2″ (12.7 mm) wide.
Figure 4-48. Interference band patterns indicate surface flatness and variations.
Optical flat
Work
Optical flat
Work
Work
Work
Optical flat
Optical flat
Concave, cylindrical
(air wedge)
Concave, spherical
(contact)
Flat surface
(air wedge)
Convex, spherical
(air wedge)
Light
source
Optical flat
Jo-block
Toolmaker's flat
Ball bearing
being inspected
Interference
bands
Interference bands
indicate difference
in size between
ball bearing and Jo-block
Figure 4-47. Optical flat set-up. Optical flat is placed on top of
the work and light is positioned above the flat.
Figure 4-49. Thickness or feeler gages.
Thickness gages are ideal for measuring narrow
slots, setting small gaps and clearances, determin-
ing fit between mating surfaces, and for checking
flatness of parts in straightening operations. See
Figure 4-50.
4.6.7 Screw Pitch Gage
Screw pitch gages are used to determine the
pitch or number of threads per inch on a screw,
Figure 4-51. Each blade is stamped with the pitch or
A B C D