The dial/vernier caliper is used to measure the inside or outside diameter of an object. Figure 2-2 shows a typical dial/vernier caliper.

Most dial/vernier calipers have a slide, slide lockscrew, thumb button, scale, dial with measured increments of 0.001 inch, and a bezel.

Figure 2-2.Typical dial/vernier caliper.

For specific instructions on how to take measurements with a dial/vernier caliper, refer to either the manufacturers instructions or to Tools and Their Uses, NAVEDTRA 10085-B2.

Regardless of what type of caliper you use, be sure to take the following precautions to avoid damaging the caliper:

1. Wash your hands before you handle the vernier caliper to remove dirt and oils that might damage the caliper.

2. Wipe the caliper components clean both before and after you use the caliper.

3. Do NOT drop or otherwise mishandle the caliper. Doing so may damage or destroy the caliper.

Figure 2-3.Measuring (A) inside and (B) outside diameters with a dial/vernier caliper.

Figure 2-3 illustrates the use of a dial/vernier caliper in measuring the inside and outside diameters of two different components.

The micrometer is a precision measuring instrument used to measure distances between surfaces in thousandths of an inch Figure 2-4 shows the most common types of micrometers.

Most micrometers have a frame, anvil, spindle, sleeve, thimble, and ratchet stop.

Micrometers are used to measure the outside diameters; inside diameters; the distance between parallel surfaces; the depth of holes, slots, counterbores, and recesses; and the distance from a surface to some recessed part. There are other uses of micrometers, but those mentioned here are uses you are most likely to encounter. Instructions on how to read a micrometer are given in the manufacturers owners manual and Tools and Their Uses, NAVEDTRA 10085-B2.

Whenever you use a micrometer, carefully observe the DOs and DONTs in the following list to obtain accurate measurements and to protect the instrument:

Figure 2-4.Common types of micrometers.

1. Always stop the work before you take a measurement. DO NOT measure moving parts because the micrometer may get caught in the rotating work and be severely damaged.

2. Always open a micrometer by holding the frame with one hand and turning the knurled sleeve with the other hand. Never open a micrometer by twirling the frame, because such practice will put unnecessary strain on the instrument and cause excessive wear of the threads.

3. Apply only moderate force to the knurled thimble when you take a measurement. Always use the friction slip ratchet if there is one on the instrument. Too much pressure on the knurled sleeve will not only result in an inaccurate reading, but also will cause the frame to spring and force the measuring surface out of line.

4. When a micrometer is not in use, place it where it will not drop. Dropping a micrometer will cause the micrometer frame to spring. If you drop a micrometer, check it for accuracy before you take further readings.

5. Before you store a micrometer, back the spindle away from the anvil, wipe all exterior surfaces with a clean, soft cloth, and coat the surfaces with a light oil. Do not reset the measuring surfaces to close contact because the protecting film of oil on these surfaces will be squeezed out.