Unknown to me, but resembles the earliest type of screw-on Stevens mounts, before Stevens came up with dovetail blocks c. 1904.  The wide flange (or rather screw head!) abutting the tube was another Stevens idea, except to work as intended Stevens flanges were separate pieces loose in the thimble that didn't rotate as the thimble was turned.   

Stevens mounts were an improvement of mounts John Sidle began making about 1890, but they weren't illustrated in any Sidle catalog I've seen, so I wouldn't know how to identify them for sure except by finding them on a Sidle scope.

marlinguy wrote on Sep 17^th, 2017 at 11:19am:


The Stevens Special scope (highest priced model in their 1903 catalog) included a rib, though on everything else the V-notch was used, as it had been previously by Sidle.   

They look well-made, although one thing I don't like about these "unknowns" is the lack of a screw to remove the spring & plunger from the outside when inserting the tube through the rings, which is the easier way to do it.

Redsetter wrote on Sep 17^th, 2017 at 1:47pm:


But wasn't the Stevens Special a later scope, and didn't it have the outside screw for the plunger you described?