Complete piston & driving blade assembly for all P250L and P250T nailers. Piston rings are wear parts that should last over 1,000,000 cycles (about 200,000 sq.ft.) under normal use. Dirt or particles in the compressed air may lessen its life. Excessive wear of the piston ring will result in occasional fasteners not set or skipped. This can be temporarily fixed with a small length of tape between the piston and the ring (never exceed one turn). It is recommended to replace this part if the tool needs to be opened for servicing and has been in use for some time. Piston assembly kits P-992N, P-992S & Q-993N : Even the toughest steel is subject to damage if driving blade hits hard surfaces. Complete piston and driving blade assembly kits are available for the most popular tool configurations: -P-992N Piston / driving blade assembly for P250L and P250T nailers -P-992S Piston / driving blade assembly for P250S stapler -Q-993N kit for the Q550 18ga nailer These kits, along with the modular engine of the P250 & Q550 pneumatic tools allow quick job-site parts replacement in just 60 seconds!