Holosun 507K is compatible with Shield RMSc/RMS/RMSw/SMS, Sig Romeo Zero Optic, or JP Jpoint Optic footprints. Is there any mounting plate that list the above optics? If so, that should be the plate. I hope this helps!

Kevin, buds has the same mounting plate you need to install the Holosun 507k on you Ruger 57 in stock and ready to ship for $26 instead of $43. Hope this helps, link to mounting plate here.......... budsgunshop.com/product_info.php/products_id/132066/ruger+97023+ruger-57+optic+adapter+plate+6061-t6+aluminum+black+hardcoat+anodized

Kevin, you need the Ruger-5.7™ Optic Adapter Plate here >>> https://shopruger.com/Ruger-57-Optic-Adapter-Plate-JPoint-Sig-Sauer-Shield-Sights/productinfo/90723/ ...Have a great day!

Kevin, you would need this Plate Sir : -- https://shopruger.com/Ruger-57-Optic-Adapter-Plate-JPoint-Sig-Sauer-Shield-Sights/productinfo/90723/