This black Bakelite plastic screw on bottom cap is what holds the blade on the bottom of the jar. Fits most Oster blenders, Osterizers and Oster Kitchen Centers. Also fits some Sunbeam models which use a metal drive pin.
ORIGINAL OSTER Replacement Jar Bottom
Not a "comparable" sold by other sellers
Includes 1 Gasket
Includes 1 Bottom base
Fits most Oster blender jars