Length (hole to hole):45mm 31mm Through hole diameter: 4.2mm Counter hole diameter: 6.3mm Screw size: M4x8mm Fits Both Milled and Stamped Receivers, such as our SCRA-21A side mount Tough Steel and designed for real fire caliber Accepts any of the european PSA, POSP Scopes with ak style side mount Consult with machinist or gunsmith for quick installation With screws and nuts