TM 1-1500-204-23-9
Figure 3-45. Surface Gauge
(1) Rule depth gauge. The rule depth gauge,
shown in figure 3-47, is a graduated rule with a sliding
head designed to bridge a hole or slot, and hold the rule
perpendicular
to
the
surface
from
which
the
measurement is taken. This type has a measuring
range from 0 to 5 inches. The sliding head has a
clamping screw so that it may be clamped in any
position. The sliding head is flat and perpendicular to
the axis of the rule and ranges in size from 2 to 2 5/8
inches wide and from 1/8 to 1/4 inch thick.
(2) Micrometer depth gauge. The micrometer
depth gauge, shown in figure 3-48, consists of a flat
base attached to the barrel of a micrometer head.
These gauges have a range from 0 to 9 inches,
depending on the length of extension rod used. The
hollow micrometer screw itself has a range of either 1/2
or 1 inch. Some are provided with a ratchet stop. The
flat base ranges in size from 2 to 6 inches. Several
extension rods are normally supplied with this type of
gauge.
(3) Vernier depth gauge. The vernier depth
gauge, shown in figure 3-49, consists of a graduated
scale, either 6 or 12 inches long, and a sliding head
similar to the one on the vernier caliper. The sliding
head is especially designed to bridge holes and slots.
The vernier depth gauge has the range of the rule depth
gauge and not quite the accuracy of a micrometer depth
gauge. It cannot enter holes less than 1/4 inch in
diameter, whereas a micrometer depth gauge will enter
a 3/32-inch hole. However, it will enter a 1/32-inch slot,
whereas a micrometer depth gauge will not. The vernier
scale is adjustable and may be adjusted to compensate
for wear.
b. Operation of Depth Gauges. The following
paragraphs describe operating procedures for each of
the depth gauge types described above.
(1) Rule depth gauge. To measure the depth of
a hole or slot with reasonable accuracy, proceed as
follows:
3-21
