The piston driver is a key part of the pneumatic coil roofing nailers funcitonality It is responsible for driving nails into the roofing material When the gun is triggered the piston thrust downwards pushing the nails out of the gun into the material Made of durable heat treated S7 steel and aerospace grade aluminum that withstand repetitive impacts 878-156 Piston Driver Replacement Part for NV45AA, NV45AB, NV45AB2M Roofing Nailer Zeluga 878-156 Piston Driver for NV45AA, NV45AB, NV45AB2M Pneumatic Coil Roofing Nailer. The piston driver is a key part of the pneumatic coil roofing nailers funcitonality. It is responsible for driving nails into the roofing material. When the gun is triggered the piston thrust downwards pushing the nails out of the gun into the material. Made of durable metal that withstand repetitive impacts.