How are they measured? From the shoulder (not including the thread) to the center of the ball. Contact point thread size is M1.7 x 0.35 Those are the measurements given below.
Why do many catalogs have different lengths from those listed below? The Interapid carbide point lengths shown in the catalogs are the length of protrusion from the front of the indicator. A useful figure in some circumstances but not particularly helpful if you have a handful of contact points and you need to sort them out. We have also listed the actual length of the point from the shoulder to the center of the ball as a reference.
Usable, exposed catalog length is the amount of protrusion (L) as shown in the sketch. The actual length is about 2 mm longer.
Ball diameter is .080" (2 mm) on new Interapid indicators. Carbide is standard with these models.
For accurate readings, Interapid contact points must be at an angle of about 12-15 degrees from the work surface. This is more critical with .0001" indicators where errors can quickly add up.