Our ball bearings was made of Chrome steel GCr15 (AISI52100) by automatic production equipment. The level of quality from ABEC-1 to ABEC-7 is available. You can get not only the good quality but also good price from us . As we are one of best manufacture of Deep Groove Ball Bearings in China 1) Series: 6000 - 6010, 6200 - 6210, 6300 - 6310 2) Shield / closure: open bearing, Z, ZZ, RS, 2RS 3) We would like to send free samples to serious buyer