Ring end gap has to be set to the engine, not to whatever the box came with, and filing a ring freehand puts a taper on the end that never seals properly. This filer holds the ring against dowel pins so the cut stays square to the face, and the hand crank gives you fine enough control to sneak up on a gap a thousandth at a time.

Proform 66785 Engine Piston Ring Filer Features:

• Files piston ring end gaps accurately to specification.
• Dowel pins hold the ring firmly and square to the abrasive wheel.
• Hand crank drives the abrasive wheel for controlled material removal.
• Use with a feeler gauge to reach the manufacturer's specified end gap.
• Sold individually.