In 6205, the basic number identifies a designation in the 62 series; 6310 belongs to the 63 series. They are different references, rather than two spellings of the same part. The catalog also distinguishes 6205-2RSH and 6205-2Z: both retain the 6205 base, but the final block is part of the identification to copy when requesting them.
The reference 6004/C3 has another structure: a basic number, a slash and an additional block. Record the entire marking, preserving hyphens, slashes and letters. Comparing only the start of a code can hide an execution difference. For replacement work, compare the designation with the removed part’s dimensions and its position in the machine; a front view photograph cannot supply all this information.
The MR catalogue lists 2,671 SKF deep groove ball bearing items. The series with the most references are 62 (831), 63 (585) and 60 (554), followed by 618 (130), 619 (97), 160 (85) and 64 (45). By execution, 515 have 2Z shields (6205-2Z), 364 have 2RS1 seals and 133 have 2RSH seals; 849 have C3 clearance.