The size of the socket on the chestnut, for connecting walnuts and other components (such as adapters and extensions) that have a socket of the same size.

Female Drive

Female receptacle chestnut, for connection with nuts and other components (e.g. adapters and extensions) that have a male socket of the corresponding size.

The number of teeth on a chestnut refers to how many teeth are on the mechanism's gear. The more teeth there are, the less movement is needed for rotation.