Patent ID: 7147232

Claim:
A workholding apparatus comprising: a body; at least one drive member carried by said body, said at least one drive member and said body at least partially defining a fluid chamber therebetween for containing a fluid; at least one driven member carried by said body, said at least one driven member having a plurality of generally circumferentially spaced apart displacement reliefs therethrough; at least one intermediate member interposed between said at least one drive member and said at least one driven member and oriented to cover all of the circumferentially spaced apart displacement reliefs of the driven member to prevent the drive member from being displaced into the displacement reliefs of the driven member, wherein at least part of a fluid chamber, and said drive, driven, and intermediate members being relatively lapped; and whereby said at least one intermediate member prevents said at least one drive member from extruding into said plurality of generally circumferentially spaced apart displacement reliefs in said at least one driven member under fluid pressures of said fluid.