Plastic micrometer (calipers) measuring device
This inexpensive plastic micrometer measures in SAE to just over 6 inches and metric up to to 155mm.
We use this same caliper in the shop to measure frames for headset size, seat post, seat clamp, hub spacing, hub measurements for spoke calculations, etc. Basically any inner or outer diameter or length that is 155mm or less.
STOP GUESSING! Save yourself time and money - get one of these today and measure first, buy once. This is an absolute must for any toolbox.