The same size can be made of different materials, including,

Stainless Steel Bearings

Chrome Steel Bearings

Carbon Steel Bearings

Ceramic Bearings

Shield / closure: Open Bearing, Z, ZZ, RS, 2RS,TT
Tolerance codes: ABEC-1, ABEC-3, ABEC-5, ABEC-7,ABEC-9
Vibration level codes: V4, V3, V2, V1
Internal clearance codes: C2, C3, C4, C5
Material: AISI52100, AISI440C, AISI304, AISI316, Ceramic
Retainer: PTFE, Nylon, PEEK Or Stainless Steel

This bearing can be found with the following part numbers on it: 
6805-2RS, 6805 2RS, 6805 RS, 6805RS, 6805-ZZ, 6805 ZZ, 6805ZZ, 6805 Z
SS6805-2RS, SS6805 2RS, SS6805 RS, SS6805RS, SS6805-ZZ, SS6805 ZZ, SS6805ZZ, SS6805 Z