Shockless, hardened steel gear train and jewel bearings
Lug on center of the back
Starrett catalog number 25-441J.
These indicators have a shockless, hardened steel gear train and jewel bearings. They are furnished with a lug on the center of the back.
This is an AGD Group 2 indicator with a 2.25" Diameter face, 0.375" shank, and #4-48 tip thread.
Chris' Tips At rest, an indicator’s needle points at a random position, usually in the 10 o’clock range. This is completely normal, as the needle’s position at rest is irrelevant to the use of an indicator.
An indicator is only useful when the tip is bearing against a surface to be measured. The action of pressing the tip against the surface moves the needle, also to some random position. But this position is relevant; turn the bezel so that the needle is pointing at zero. Now you can make measurements, both positive and negative, relative to the starting position.AGD Groups define the size of the indicator.
1.00 - 1.38"
25 - 35 mm
1.38 - 2.00"
35 - 50 mm
2.00 - 2.38"
50 - 60 mm
2.38 - 3.00"
60 - 75 mm
3.00 - 3.75"
75 - 95 mm
Inch indicators have a 0.375" diameter shank with a #4-48 thread for tips. Metric indicators have an 8 mm diameter shank with an M2.5 thread.