This shim kit contains 2 pcs 0.5mm stainless steel shims in order to add 1mm to the mounting span of your needle bearing kit. This particular kit is for 6mm OD mounting bolts. It is for the following needle bearing kits when used with a 6mm bolt:

NBKRWC1905
NBKRWC30
NBKRWC3383
NBKRWC3556
NBKRWC38
NBKRWC3988
NBKRWC4115
NBKRWC4374