The 167/688 quad mini bearing adapter is made of aluminum. The bearing adapter fits over your 167 or 688 mini bearings so they can be used in a 608 wheel hub. You will need 1 adapter per wheel.
There are two advantages to using mini bearings.
1. You create a much lighter setup as a 608 bearing weighs 12 grams compared to a mini bearing at 4 grams and an adapter at 1 gram.
2. Mini bearings spool up faster than regular 608 bearings.
You need 1 adapter per bearing.
Sold individually (1 adapter)