These units are sold in pairs. -Bronze bushing lubricates piston- no binding! 5/8" body- smaller hole needed than other brands Body pressed together- no bolts to come loose! Brass piston/ stainless striker plate- Cleaner and longer wearing than aluminum These units are sold in pairs. These door poppers- they're simple, but they're NOT all made the same! Here are just a few advantages with our new poppers: -Bronze bushing lubricates piston- no binding! -Body pressed together- no bolts to come loose! -Brass piston/ stainless striker plate- Cleaner and longer wearing than aluminum -5/8" body- smaller hole needed than other brands -All mounting hardware easily concealed with included cap!