On both spring perch center bolt holes. Bought some new center pins for the zero-rates I have to install on some springs and the round heads look a little big in diameter. I don't have a D60 laying around without springs on it and now need you guys who do, to get a quick spec on both holes for me. I may have to grind a little bit of material off the head, don't know for sure yet until I can measure both. TIA.