Bore code

The bore code is formed by the last two digits of a rolling bearing's basic designation. From code 04 upwards, multiplying by 5 gives the bore in millimetres: a 6204 has a 20 mm bore, a 6310 a 50 mm bore. Four exceptions apply below that: 00 = 10 mm, 01 = 12 mm, 02 = 15 mm, 03 = 17 mm. For bores under 10 mm the diameter appears directly in the designation (e.g. 608 = 8 mm); intermediate bores are appended after a slash (e.g. 62/28 = 28 mm). The code is uniform across manufacturers and the quickest way to identify an unknown bearing.