Patent ID: 7370746

Claim:
A ball transfer unit comprising: a) a main body having a seat surface recessed in a semispherical shape; b) a plurality of small balls which are each in freely rolling contact with the seat surface of the main body, c) a large ball which is in freely rolling contact with the plurality of small balls, and d) a cover which is attached to the main body and is adapted for holding the large ball and for holding the small balls between the large ball and the seat surface of the main body; wherein at least the main body and the large ball are made of a material selected from among PAI, PBI, PCTFE, PEEK, PEI, PI, PPS, melamine resins, aromatic polyamide resins, aluminum oxide, zirconium oxide and silicon nitride; wherein the main body, the small balls, and the large ball each have a Rockwell hardness H R R of at least 75.