I’ve measured the pitch on a handful of vintage lenses. The usual range is about 0.1 to 0.2 mm per full turn, so a half‑turn gives you roughly 0.05 to 0.1 mm. The trick is to use a digital caliper or a fine‑tipped ruler. Mark a reference point on the ring, count ten full turns, measure the linear distance, then divide by ten. That gives you the pitch to the nearest hundredth of a millimeter. If the ring feels like a puzzle, you’re probably dealing with a 1/4‑inch thread, which is common on many 70s lenses. Once you know the pitch, the whole “step” mystery disappears.