Gunson thread gauge, £9
Time tested: 12 months
What's good? I'm (still) working through an old Kawasaki KR-1S, fixing the bodges I made 20 years ago and replacing the worst of the abuse. Before I order new bolts I push the old ones through the holes of this aluminium gauge to check thread diameter, and then measure thread pitch using the calibrated teeth on the gauge's outer edge. It's very quick and unexpectedly satisfying. This set of four discs also measures spark plug threads and US sizes.
What's not? Children use them as Ninja throwing stars.
Quality rating: 3/5
Value rating: 4/5