Mushroom pin

A mushroom pin, “pin en champiñón” in Spanish, is a security pin shaped like a mushroom: a wider head and a narrower neck. It is normally fitted as a driver pin, in the upper part of the chamber.

Its defence lies at the shear line. During an attempt to open the lock with a pick, the narrow neck catches on that edge and gives the false impression that the pin is already in place, when in fact it is still blocking.

With the correct key the pin rises to its height and you notice no difference at all.

It is one of the most widespread security pins and is usually combined with spool or serrated pins in the same cylinder. On its own it does not make a high security cylinder, but it is a minimum you should insist on. Ask what yours has under security cylinders.