Basic Model: Measure the diameter of the Dial in inches, Also note if there is a screw or "bolt head" in the back. This determines if it can be adjusted or "resettable". Also note the mounting of the stem. the choices are: back, bottom and adjustable angle. You may also find some with left or right hａnd mounting, but these are less common. Select the Model from the following Table.
General Specifications
| Model | Dial Size | Connection | Resettable |
| 20 | 2" | Back | No |
| 30 | 3" | Back | Yes |
| 31 | 3" | Bottom | Yes |
| 32 | 3" | Adjustable | Yes |
| 33 | 3" | Back | No |
| 34 | 3" | Bottom | No |
| 50 | 5" | Back | Yes |
| 51 | 5" | Bottom | Yes |
| 52 | 5" | Adjustable | Yes |
| 53 | 5" | Back | No |
| 54 | 5" | Bottom | No |
Stem Length: Measure the stem from the top of the threaded connection to the end of the stem. The standard lengths in inches are: 2.5, 4, 6, 9, 12, 18, 24, 30, 36, 42, 48, 54, 60, 66, 72. The length is specified as XXX; 2.5" = 025; 72" = 720
