The tappet follower which was designed (right) after the Norton factory decided to move away from having a lever type tappet was good for several years from the post-war era until they had a minor re-design for the alternator models. It is not difficult to see why the design had a much more substantial thickness as any attempt to remove the thinner item would break the casting....as the factory must have discovered themselves.
When Pierre Vernier invented the vernier scale he must have known he was onto a good thing. As I belong to the generation of people who used slide-rules before calculators came along the idea is very familiar. However just as slide rules were referred to a 'guessing sticks' so vernier callipers were called " very- near" callipers. The big change was when they became digital and I now use it constantly.