| Screw thread micrometers measure the pitch of the thread directly. The screw thread micrometer has a 60-degree pointed spindle and a double V-shaped swiveling anvil (Figure 1). |
|
|
|
The screw thread micrometer reading indicates the pitch diameter of the thread. When the micrometer is set at zero, the pitch line of the spindle and anvil coincide (Figure 2). When the micrometer is measuring the thread, it is measuring along the pitch diameter of the thread (Figured 3). |
| Fixed anvil screw thread micrometers are those types of screw thread micrometers that can only measure thread pitches within a limited range. It is important to make sure that the screw thread micrometer that you will be using falls within the screw pitch range of a particular thread. With fixed anvil screw thread micrometers, seven micrometers will be needed to cover threads from 3 to 64 threads per inch. |
|
The type of screw thread micrometer shown in Figure 4 has interchangeable anvils to cover a wide range of thread pitches. Whenever you change the anvils on the thread pitch micrometer, check the micrometer for accuracy.
| Figure 4 1–2 inch screw thread micrometer with interchangeable anvils |  |
 |
Figure 5 Set of interchangeable anvils for an interchangeable anvil screw thread micrometer. |
