Review on Woodworking Stainless Measuring Waterproof Carpenter by Mark Bearden

These are cheap and handy pressure gauges that measure both internal and external dimensions with the same tool. For precision work, don't rely on the indicator, use it as a caliper and then measure between points. Decently made for the price and easily adjustable in tension so they're easy to adjust, or stiff enough that they don't move while you're taking a reading. They'll never be mistaken for Starrett quality, but they're good enough for most uses and cheap enough that you can toss them on the top shelf of your toolbox and save the expensive ones for the store.