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In a fastener driving tool, a retention system for a piston comprises a buffer and a set of bearings in a cage, the bearings being abutted against the buffer. The buffer provides a force urging the bearing radially inwardly toward the piston so that the bearings retain the piston in a predetermined

In a fastener driving tool, a retention system for a piston comprises a buffer and a set of bearings in a cage, the bearings being abutted against the buffer. The buffer provides a force urging the bearing radially inwardly toward the piston so that the bearings retain the piston in a predetermined position when the piston is not being actuated.

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1. A piston buffer and retention system for a fastener driving tool comprising: a resilient plastic buffer for absorbing shock from a piston traveling in an axial driving direction; and a set of bearings retained in a cage, the bearings being abutted against the buffer and spaced radially betwee

1. A piston buffer and retention system for a fastener driving tool comprising: a resilient plastic buffer for absorbing shock from a piston traveling in an axial driving direction; and a set of bearings retained in a cage, the bearings being abutted against the buffer and spaced radially between the buffer and the piston; wherein the buffer provides a radial force urging the bearings radially inwardly toward the piston so that the bearings retain the piston in a ready-to-fire position prior to firing. 2. A retention system according to claim 1, wherein the buffer is made of urethane. 3. A retention system according to claim 1, wherein the bearings are generally spherical in shape. 4. A retention system according to claim 1, wherein there are at least three bearings. 5. A retention system according to claim 1, wherein the bearings are evenly spaced around the periphery of the piston. 6. A retention system according to claim 1, wherein said cage and said bearings are spaced radially between said buffer and said piston. 7. A tool for driving fasteners comprising: a piston guide having a barrel; an actuable piston retained in the barrel to drive a fastener in an axial driving direction into a substrate; means for driving the piston in the axial driving direction; a piston buffer and retention system including a resilient plastic buffer retained in the barrel for absorbing shock from the piston and a set of bearings retained in a cage, the bearings being abutted against the buffer and being spaced radially between the buffer and the piston; wherein said piston buffer and retention system is replaceable as an assembly; and wherein the buffer provides a radial force urging the bearings radially inwardly toward the piston so that the bearings retain the piston in a ready-to-fire position prior to firing the tool. 8. A tool according to claim 7, wherein the piston is driven by gasoline combustion. 9. A tool according to claim 7, wherein the piston is driven by explosive powder. 10. A tool according to claim 7, wherein the buffer is made of urethane. 11. A tool according to claim 7, further comprising a muzzle bushing having a through bore for guiding the piston. 12. A tool according to claim 11, wherein the muzzle bushing is releasably connected to the piston guide. 13. A tool according to claim 11, wherein the muzzle bushing and the piston guide are threaded. 14. A tool for driving fasteners comprising: a piston guide having a barrel; an actuable piston retained in the barrel to drive a fastener in an axial driving direction into a substrate; a combustion chamber for exploding powder to drive the piston in the axial driving direction; a piston buffer and retention system including a resilient plastic buffer retained in the barrel for absorbing shock from the piston and a set of bearings retained in a cage, the bearings being abutted against the buffer and being spaced radially between the resilient plastic buffer and the piston; wherein said piston buffer and retention system is replaceable as an assembly; wherein the buffer provides a radial force urging the bearings radially inwardly toward the piston so that the bearings retain the piston in a ready-to-fire position prior to firing the tool. 15. A tool according to claim 14, wherein the buffer is made of urethane. 16. A tool according to claim 14, further comprising a muzzle bushing having a through bore for guiding the piston. 17. A tool according to claim 16, wherein the muzzle bushing is releasably connected to the piston guide. 18. A tool according to claim 16, wherein the muzzle bushing and piston guide are threaded.