This is a Bearing NJ308 C3 for a National vacuum challenger 607 pump. This part fits all National Vacuum 607 PRO Challenger Series vacuum pumps.
This is diagram part #10 on the 607 PRO fan cooled pump exploded view and diagram part #10 on the 607 PRO liquid cooled pump exploded view.
The National Vacuum Equipment Part Number is 120-019-367