Rexroth Tightening System 300 Interface Modules SMpdp: Interface for connection of the tightening system to Profibus DP. SMibs: Interface for connection of the tightening system to Interbus-S. SM24V: Interface used for activation of the tightening system via 24V signals and accordingly for the output of 24V signals out of the tightening system. SMser: Used for data communication with the tightening system via RS232 / RS422 or 20mA interface. SMeth: Used for data communication via Ethernet interface.