Here's how it works on pre-1960 Savage 99's. The rear screws into the two existing tang screw holes, and the front slides into the rear sight dovetail and locks down with a tightening screw. Then you can mount any rings and scopes you like.

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“The Savage 99 Pocket Reference”.
All models and variations of 1895’s, 1899’s and 99’s covered.
Also dates, checkering, engraving.. Find at www.savagelevers.com