Cummins ISX12 Engine Brake Adjustment Tool 3.4MM 5298757 Jake Brake Feeler Gauge Features: 1. Application: For Cummins ISX 12 diesel engines 5298757 Jake Brake Feeler Gauge Shim Alt. 2. OEM #: Engine brake adjustment tool 3.4 MM alternative to # 5298757. The 3.4mm area is precision ground to +/- .0005 inch. 3. Advantage: This angled feeler gauge to allow easier insertion between slave pistons contact surface with the exhaust valve adjusting screw. ( Straight feeler can be bent easily) 4. Benefits: .