The MAS is the combination of number of previous semi smart relays. These relays carried the loads for most of the high current users involved with the engine. These relays include, fuel pump, A/C clutch, AIR pump (smog pump)clutch and at least one other user I can't recall.
Because of the large number of contacts and previous problems with these circuits MB designed a relay that would "screw" itself into the connector. That is the purpose of the knob. One direction it unsockets the relay the other way it inserts itself.