Full ceramic (ZrO2) bearings. (Set of 2) *Other sizes are also available. (If you purchase multiple items, we will offer a small discount.) ↓ Specifications Size standard: MR115 (also known as 1150) Outer diameter: 11mm Inner diameter: 5mm Thickness: 4mm Examples of suitable models: Revo Big Shooter Salty Stage Revo LJ-1, LJ-3 Morrum SX High Speed 1500C 1600C 2500C 2600C 3500C etc. *However, please make your own judgment regarding compatibility. 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 become a little quieter.) However, because it is full ceramic (PTFE for the ball retainer), there should be no seizure like that of bearings with metal cages & metal balls, even in the spool rotation range of a bait reel (even in dry condition). In other words, it does not rust (even when used in saltwater), and it is an ideal maintenance-free bearing (at present) that does not require lubrication. 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.