This cap is used on many 4 cylinder BMC engines fitted to the MGB, Midget, Sprite and many others. It is similar to the Lucas GDC136 cap. It is a push fit cap, held on by spring clips, with push fit high tension lead sockets. Distributor caps can develop faults which are difficult to see with the naked eye. This causes misfiring, often only when the engine is under load, so it will tick over sweetly but becomes rough under acceleration.