6901 is the bearing size, 2RS refers to the removable rubber seals on each side. Probably all radial ball bearings you'd find on a mountain bike are 2RS. See here, for example: [https://www.bearingcentre.net/blog/which-bearing-closures-are-best](https://www.bearingcentre.net/blog/which-bearing-closures-are-best)
Jan. 19, 2022, 11:26 a.m. - toddball
6901 is the bearing size, 2RS refers to the removable rubber seals on each side. Probably all radial ball bearings you'd find on a mountain bike are 2RS. See here, for example: [https://www.bearingcentre.net/blog/which-bearing-closures-are-best](https://www.bearingcentre.net/blog/which-bearing-closures-are-best)