There are two different methods of giving you the micrometer 'click' when you rotate the range adjustment spindle. Some rearsights were supplied with a little plunger that the tiny spring fits over (& both together fit into the little hole at top left of the sight leaf). Others have the spring, but have the ball bearing instead of the little plunger. If you have one of these sights you just need to seat the ball bearing on top of the spring in its little hole, with a blob of grease. Then do as L1A1 breakdown has explained.