Question

what are shims used for?
to achieve the correct clearance between the pinion gear and flywheel ring gear
to reduce the amount of heat generated by engaging the flywheel ring gear
to smooth rough edges of the ring gear
used to lubricate the pinion gear and engage the flywheel

Explanation:

Shims are thin pieces used to adjust spacing or clearance. In the context of gears, they are used to set the correct distance between the pinion gear and fly - wheel ring gear for proper meshing and function.

Answer:

To achieve the correct clearance between the pinion gear and flywheel ring gear