Full ceramic (ZrO2) bearings. (Set of 2, different sizes) ↓ Specifications below ※ Other sizes are also available. (If you purchase multiple items, we will offer a small discount.) Please comment if you would like to make a proposal. [Palm cup side] Size standard: 623 (commonly known as 1030) Outer diameter: 10mm Inner diameter: 3mm Thickness: 4mm [Spool (shaft) side] Size standard: MR105 (commonly known as 1050) Outer diameter: 10mm Inner diameter: 5mm Thickness: 4mm Examples of compatibility... [ABU] Black Max (old) Silver Max (old) Pro Max (old) [DOVIELLO] HIAW200 ※ Chinese-made, sold on Amazon etc. It's a good quality reel. It also has a low gear (5.4:1) setting, and is a value cranking machine. (I have confirmed the installation & rotation with this.) Please refer to the 3rd image for the spool shaft section. Others, mainly Chinese-made bait reels etc. (SEASiR etc.) ※ The above is for reference only, so please confirm the size compatibility at your own responsibility. It rotates most smoothly when used dry, but when incorporated into the spool system of a bait reel, a high-pitched "shhh" sliding noise will occur during casting. If you are concerned about this, please apply an appropriate amount of oil. (It should become a little quieter.) ※ However, because it is full ceramic (PTFE for the ball retaining parts) (Even in a dry state) at the rotation range of a bait reel spool, there should be no seizure like that of a metal cage & metal ball bearing. In other words, (even when used in saltwater) it will not rust, and it is an ideal maintenance-free bearing (at this time) that does not require oiling 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.