The 2nd Generation Henry Big Boys have a reciever that is already drilled and tapped for this scope mount. This rail is a Picatinny style cut with multiple cross slots ready for mounting Weaver or Picatinny style rings. 2nd Generation Big Boy rifles are drilled and tapped on the receiver for this scope mount. If your Big Boy rifle lacks these receiver screw holes it is most likley a Gen 1 and will need the Gen 1 scope mount.Gen 2 Big Boys start with the following serial numbers: H006 - BB0047222 H006M - BB0015530M H006C - BB0021188C