This ADE RD3-006, alone with RD3-009,RD3-012,RD3-013 do NOT fit Springfield HELLCAT OSP, because springfield Hellcat OSP red dot footprint is based on Shield RMS. ADE sights has the footprint of Doctor/Vortex Venom type footprint. This RD3-006, and RD3-009, RD3-012 and RD3-013 fits directly to "Optics Ready" pistols such as Glock MOS, Springfield OSP(non-hellcat), Canik TP9 SFX(non elite sc), Walter PPQ Q5 Match, FNX 45 Tactical, IWI Masada handguns that come with mounting plates that marked for DOCTOR/VORTEX VENOM type red dot. All mentioned above pistols must to be OPTICS READY model that comes with MOUNTING PLATE marked for DOCTOR/VORTEX. If not, user has to purchase after market mounting plate(not included with this red dot sight purchase) to replace the rear sight. When you first receive the red dot. It has a picatinny mounting plate pre-assembled. Please use allen wrench provided to take out the 2 hex screws on the top behind the glass frame. It will disconnect the red dot from the picatinny mounting plate. You will then be able to attach the red dot to a variety of handgun mounting plates that are sold separately. There are many popular handguns on the market, due to the size difference of the handguns, each mounting plate is slightly different in dimensions. There are also many manufacturers making a variety of handgun plates that replace the rear sight, including ADE, Lakeline LLC, EGW, and Outerimpact. The screw comes with our red dot come with a pair of M3x6mm screws to connect to the pre-assembled picatinny mounting base. Some mounting plates made by other companies for specific handgun might need a longer screw such as M3x8mm or shorter screw such as M3x4mm depends on the thickness of the mounting plate/adapter. If you can't get the screw to work properly, we recommend going to a local hardware store such as ACE Hardware to get the right size.