(e) Measure the length of the micrometer
test gauge of the same length as the maximum capacity
of the micrometer.
(f) The micrometer should read its exact
i. Care of Micrometers. Observe the following
practices for the care and upkeep of micrometers:
(1) Coat metal parts of all micrometers with a
light coat of oil to prevent rust.
(2) Store micrometers in their separate
containers provided by the manufacturer.
(3) Keep graduations and markings on all
micrometers clean and legible.
(4) Never drop any micrometer. Small nicks or
dents can cause inaccurate measurements.
3-10. Surface Gauge. A surface gauge is a measuring
tool used to transfer measurements to work by scribing
a line, and to indicate the accuracy or parallelism of
a. Description. As shown in figure 3-45, the surface
gauge consists of a base with an adjustable spindle to
which may be clamped a scriber or an indicator. Surface
gauges are made in several sizes and are classified by
the length of the spindle. The smallest spindle is 4
inches long, the average 9 to 12 inches, and the largest
18 inches. The scriber is fastened to the spindle with a
clamp. The bottom and the front end of the base of the
surface gauge have deep V-grooves. The grooves allow
the gauge to measure from a cylindrical surface. The
base has two gauge pins. They are used against the
edge of a surface plate or slot to prevent movement or
b. Adjustment. The spindle of a surface gauge may
be adjusted to any position with respect to the base and
tightened in place with the spindle nut. The rocker
adjusting screw provides for the finer adjustment of the
spindle by pivoting the spindle rocker bracket. The
scriber can be positioned at any height and in any
desired direction on the spindle by tightening the scriber
nut. The scriber may also be mounted directly in the
spindle nut mounting, in place of the spindle, and used
where the working space is limited and the height of the
work is within range of the scriber.
c. Setting Height on a Surface Gauge. To set a
surface gauge for height, proceed as follows:
(1) Wipe off the top of a layout table or surface plate
and the bottom of the surface gauge.
(2) Place the squaring head of a combination square on
a flat surface as shown in figure 3-46.
If a combination square is not available,
use a rule with a rule holder. A rule alone
cannot be held securely without wobbling,
and consequently an error in setting
(3) Secure the rule in the squaring head so that
the end of the rule is in contact with the surface.
(4) Move the surface gauge into position, and
set the scriber to the approximate height required, using
the adjusting clamp that holds the scriber onto the
(5) Make the final adjustment for the exact
height required with the adjusting screw on the base of
d. Care of Surface Gauge. Observe the following
practices for the care and upkeep of surface gauges:
(1) Coat all metal parts of the gauge with a light
coat of oil to prevent rust.
(2) Carefully store the gauge in the separate
container provided by the manufacturer.
(3) Do not drop any surface gauge. Small nicks
and scratches can result in inaccurate measurements.
(4) Protect all pointed parts from damage.
3-11. Depth Gauges. Depth gauges are used to
measure the distance from a surface to a recessed
a. Types. The three common types of depth
gauges are the rule depth gauge, the micrometer depth
gauge, and the vernier depth gauge.