With all the various manufacturers of housings, shafts, lockers and gears ... sometimes things don't line up.
Some things do play perfectly together but often times you have slop and play between components that can lead to premature failures or unexpected handling characteristics.

This shim kit is designed to help remove that slack in multiple axle and differential setups.

The smaller shims can help remove play in axle shafts and pinion that ride on 5mm inner diameter bearings.
The larger shims work well for differentials and some front knuckle setups that use 10mm inner diameter bearings.

Each kit includes 4 shims:
8 x 5 x 0.3mm (2)
13 x 10 x 0.3mm (2)

The kit is designed around Axial based axles and differentials, but will fit various applications.

Shown on an OT Shaft with bearing and FI Spool for reference (parts not included):