Full Ceramic (ZrO2) Bearings. (Set of 2) *Other sizes are also available. (If you purchase multiple items, we will offer a small discount.) ↓ Specifications Standard Size: MR104 (also known as 1040 size) Outer Diameter: 10mm Inner Diameter: 4mm Thickness: 4mm Examples of suitable models include: Abu Garcia Revival Edition Ambassador 4600C 5500C 5600C 6000C 6500C etc. *However, please determine compatibility at your own risk. They rotate most smoothly when used dry, but when installed in the spool system of a bait reel, a high-pitched "shhh" sliding noise may occur during casting. If you are concerned about this, apply an appropriate amount of oil. (It should become a little quieter.) However, because they are full ceramic (PTFE for ball retainers), there should be no seizing like that of metal cage & metal ball bearings (even in a dry state) at the rotational speeds of a bait reel spool. In other words, (even when used in saltwater) they will not rust and require no lubrication, making them (at present) ideal maintenance-free bearings. Because they are non-magnetic, they are easy to install near brake magnets. Please note that after installing them in a reel, you may not be able to receive manufacturer warranty, so please use them at your own risk.