The common stainless insert bearing is AISI 420 & 440C (having magnetic properties).Other stainless steel materials can be used such as AISI 304 etc.
AISI 304 stainless steel insert ball bearings have much greater corrosion resistance than those made of SAE 52100 bearing steel , AISI 420 or AISI 440C stainless steel.Heat resistant grease is used in AISI 304, AISI 420 and AISI 440C stainless steel ball bearings.