Full Ceramic (ZrO2) Bearings. (Set of 2, different sizes.) *Other sizes are also available. (Discounts available for multiple purchases.) ↓ Specifications below [Palm Cup Side] Size Standard: 623 (also known as 1030) Outer Diameter: 10mm Inner Diameter: 3mm Thickness: 4mm [Spool (Shaft) Side] Size Standard: MR115 (also known as 1150) Outer Diameter: 11mm Inner Diameter: 5mm Thickness: 4mm Examples of Compatibility: [Shimano] 22 Metanium Shallow Edition 20 Metanium 16 Metanium MGL 19 Antares 18 Antares DC MD XG 16 Antares DC 18 Bantam MGL 21 Scorpion MD 21 Calcutta Conquest 15-18 Calcutta Conquest 300-400 15-16 Ocea Conquest 300 17 Exsence DC etc. [Daiwa] 22 Zillion TW HD 18 Zillion TW HD Zillion TW Zillion HD Zillion TWS Steez (1st generation) Steez A TW Ryoga (1st generation) Ryoga Bay Jigging 15 Ryoga Shrapnel 18 Ryoga 21 Tatula TW 300, 400 18 Catalina TW Morethan PE TW/SV etc. [ABU] Revo series, etc. *The above is for reference only, please confirm the size compatibility at your own risk. It rotates 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 quiet down a bit.) *However, because it is full ceramic (PTFE for the ball retaining parts), there should be no seizing like with metal cage & metal ball bearings (even in dry conditions) at the rotational speeds of a bait reel spool. In other words, it is a (currently) ideal maintenance-free bearing that does not rust (even when used in saltwater) and does not require lubrication, etc. Because it is a non-magnetic material, it is easy to install near the brake magnet. Please note that after installing it in a reel, you may not be able to receive manufacturer's warranty, so please do so at your own risk.