Bit key

A bit key is a key with a round shank and a flat blade at the tip, the bit, which carries the cuts. As it turns inside the lock, those cuts move the internal parts and let the bolt slide.

It is the typical key for lever locks, although it is also found on other old locks. There are single bit keys, with one blade, and double bit keys, with a blade on each side.

It is easy to recognise: a long key, round in the shank, with the blade at the end. If the one for your door looks like this and the lock has a few years on it, it is worth knowing that there are safer options today that can be fitted without changing the door. You can see them in lever lock to cylinder conversion.