All three types are nonmetallic (phenolic). A223/A224 -Plain phenolic bore are used as quide and secondary control pulley in production aircraft. AN210: Similar to MS24566, but have metal shielded bearings rather than removable composition seal type bearings. MS20219: Nonmetallic sheave and fixed ball bearing. MS20220: Flight control pulley, non-metallic sheave and fixed ball bearing with contact seal. MS24566: Anti- friction bearing pulley.