This is a four pack replacement set of sand domef for an N Scale OEM Bachmann PRR K4 dome. Once the OEM dome is removed, this design can fit the original holes using the pins and glued in place. As an alternative the pins can be shaved off and the center boss tapped for a 00-90 screw. Then the part can be installed after a 00-90 clearance hole is drilled in between the two original boiler shell holes to accept a short 00-90 screw. See pic.