And OS material is ??
ABL = Alluminum Brass Lithium ???
OS says Advanced Bimetallic Liner and only refers to two layers of nickel although its cylinder is made of brass.
Not all acronyms are used same way by manufacturers.

Saito 56 is AAC but it has ring at piston. OK it's a four stroke but it is'n a tappered cylinder. There are other brands with four stroke ABC type engines without ring and tappered cylinders.