SVD Dragunov gas system piston. This is one part in your Dragunov that is experiencing wear even if you fire your rifle once. IHMO, if you like to take your rifle shooting once in a blue moon, why not to have a spare part for the one takes one of the worst beating in it. This way you can replace the part you used, and have the virgin one on the side, just in case if you need to sell the rifle.