Our bearings are deep groove ball bearings, 8mm single row radial ball bearings precisely, and consist of the following parts:
Outer ring — 52100 chrome steel ring, flat on the outside, with polished and hardened raceways on its inside
Inner ring — 52100 chrome steel ring, flat on the inside to fit axles, with polished and hardened raceways on the outside
Balls — 6 of them, heat treated 52100 chrome steel for increased hardness (Decode GOLD) or Si3N4 ceramic (Decode CERAM1K)
Retainer/cage — Nylon composite, holding the balls in place
Shields — Rubber coated steel, protecting your bearings from dust and dirt. RZ means, the bearings have one rubber coated shield.