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Yes they should according to reloaderaddict.com the RIA 1911 will accept a Novak low mount low mount dovetail cut (same as these sights are) https://www.reloaderaddict.com/best-rock-island-1911-sight-upgrade-night-sight-replacement-armory-review/

John, I would contact Rock Island Armory for their Dovetail front and rear slot sizes for the RIA Ultra FS 9mm 5 inch (51623) at Phone: (775) 537-1444 or by online Inquiry here : https://www.armscor.com/support-center/contact-support/ --------------- The dimensions of these Dovetail Sights are Fronts are .330" x 65 degree dovetail - Rears (Fixed LoMount Carry) are .495" x 65 degree dovetail - Front blade width: 0.144" - Front blade height: 0.290" - Rear sight width: 0.169" - Rear Height: 0.485".