Super budget calipers
won't scratch the thing you are measuring and
are easy to find in their snazzy red plastic.
seem fairly robust and once you get used to it, the vernier scale is easy to read.
measure inner and outer size at the top
depth at the bottom and step above the sliding top jaw.
these have a vernier scale it gives tenths of a mm
Basic digital calipers
plastic non scratching
metric or imperial
requires a battery