Bearing size is 3 x 10 x 4mm. Stainless steel balls. Fits all newer style Shimano casting reels with bearing part #BNT0194, BNT0084, and TGT0184. These bearings are incredibly fast and are our NEW STYLE bearings with one side unshielded! This is to facilitate easier cleaning. Just turn the open side towards the inside of the reel or spool and it's still protected. They come shipped bone dry with no oil in them. If you find them to be too fast, you can add a small drop of your favorite bearing oil to slow them a bit. Heavier oil will slow the bearing even more if desired. Ball bearings are rated in a classification system know as ABEC....Annular Bearing Engineering Committee. Bearings in the ABEC system are all called 'precision bearings' and rated from 1 to 9, 9 being the highest precision. The numbers jump from 1 to 3 to 5 to 7 to 9. A 'standard' bearing is an ABEC 1, a super expensive bearing is an ABEC 9. Shimano's come stock with an ABEC 3 bearing in them. Any ?'s regarding fit, please either Contact Us or see our Schematics Pages Kit contains 2 bearings.