Siemens 6ES7921-3AH00-1AA0 Automation Connection Component — Legacy Replacement. Siemens 6ES7921-3AH00-1AA0 is the exact manufacturer order number for a automation connection component in the SIMATIC S7-300 Connection System portfolio. Siemens describes this exact reference as: ********** spare part ********* SIMATIC S7-300, front connector for crimp contacts, without crimp contacts 20-pole, PU=100 units. The verified manufacturer lifecycle record is PM410:Product cancellation.