this is a piston for a fastener gun tool. Hilti is probably the largest manufacturer of fastener nail guns. I used one for a long time and remember cocking the gun to prepare to reload. a nail would be placed in the barrel and held in place by a plastic ring on the nail that would friction fit into the barrel. This piston would be shot into the nail head and drive the nail into whatever, and I mean whatever! wood, concrete, steel beams , whatever! This piston is very hard, would get almost polished on the tip and get carbon deposited on the sealing ring end. Hilti salesman may be able to pinpoint the exact application and part # of your piston. The pictures give details but not exact dimensions. pistons are for sale on ebay and other sited as well. google image, hilti piston Jerry

this is a piston for a fastener gun tool. Hilti is probably the largest manufacturer of fastener nail guns. I used one for a long time and remember cocking the gun to prepare to reload. a nail would be placed in the barrel and held in place by a plastic ring on the nail that would friction fit into the barrel. This piston would be shot into the nail head and drive the nail into whatever, and I mean whatever! wood, concrete, steel beams , whatever! This piston is very hard, would get almost polished on the tip and get carbon deposited on the sealing ring end. Hilti salesman may be able to pinpoint the exact application and part # of your piston. The pictures give details but not exact dimensions. pistons are for sale on ebay and other sited as well. google image, hilti piston Jerry

References:

http://www.ebay.com/itm/Piston-To-Fit-Ramset-Cobra-Hilti-DX350-Powers-P3500-S...