Found this in a box of goodies at the gun shop, but no idea what it fits.
It has two levers to disconnect the rings. Flat bottom so I assume it fits another base.
5 3/8 long with three mounting screws.
Does anyone have an idea what this fits?

Marlin 1895/336

https://www.leupold.com/qr-marlin-1895-336-1-pc-matte

Thank you mystery solved.

Those Leupold Quick Detachable rings aren't the prettiest or fanciest, but I've been impressed with how strong and repeatable they are. I've used them on a .416 Rem. and a .460 Wby for over 20 years and have had no problems.

Try a rem 788

Leupold QD for Marlin 95, 336s, a very nice mount and they work, but don't tighten them with pliers as a guy I know showed up here wanting to know who could weld the lever back on!! I suggested he contact Leupold for replacement.