The Saracen 4 gearbox attaches to extension pieces via serrated connections, also known as crocodile teeth fixings.
This 20mm backset variant has the code 05060 on the shoot bolt extension sockets to distinguish it from its cranked counterpart.
These gearboxes are available with a 9.5mm deadbolt. The 11.5mm and 13.5mm deadbolt variations are discontinued.
They are sometimes stamped "AUBI".