Drive sprocket device

A drive apparatus for a chain saw, comprising:

• a drive sprocket rotatable about an axis of rotation and including an outer surface of a first diameter which includes circumferentially spaced recesses;
• a drive ring assembly comprising a pair of separate drive rings loosely mounted for rotation on said drive sprocket, each drive ring being circular and extending endlessly in a circumferential direction, said drive rings including respective circumferentially extending portions spaced apart by a first axial distance to form an annular space therebetween, each circumferentially extending portion having radially spaced outer and inner surfaces, said inner surface having a second diameter larger than said first diameter, whereby a center axis of each drive ring is offset from the axis of rotation of the drive sprocket;
• a saw chain extending around said outer surfaces of said drive rings and including drive links extending radially inwardly through said annular space;
• and
• first and second radial stop surfaces spaced apart in a direction parallel to said axis of rotation by a second axial distance to form an axial space in which said first and second drive rings are disposed, said stop surfaces being fixed in axially spaced relationship for limiting a maximum axial separation between said first and second drive rings to a distance slightly larger than a thickness of said drive links.