Feeler gauge

A feeler gauge (in Spanish, galga de medición) is an instrument with blades or templates of known size, used to check a gap, a thickness or a profile quickly. The most common is the thickness gauge set: several steel blades of different thicknesses that are slid into a gap until you find the one that fits exactly.

The locksmith uses it to measure the gap between the door leaf and the frame, check whether a door closes evenly at the top and the bottom, verify the thickness of a metal sheet or compare a part with its factory dimensions.

A large gap between the door leaf and the frame is a bad sign, because a lever can be pushed in there, and it usually points to a door that has dropped. If you want to know the size of your lock cylinder without special tools, use the calculator to measure the cylinder.