Cantilever mount
A one-piece mount whose rings sit forward of the rail clamp, usually about 2 in. It moves the scope forward so a thermal's short eye relief works on an AR-15's flat-top rail.
What it means
A cantilever mount is one solid piece: a base that clamps the rail and an arm that holds the rings out in front of it. The forward reach is the offset. Most cantilever mounts are offset about 2 in (51 mm); makers usually print it.
What it changes in the field
- Eye relief on an AR. An AR-15’s rail ends over the receiver. Thermal scopes often have short eye relief, so without the offset the eyepiece can sit too far forward of your eye.
- One-piece rigidity. The two rings cannot be misaligned the way separate rings can.
- Height. Cantilever mounts for ARs are tall, to line the scope up with an upright head on a straight stock. Most of the ones on this site publish a height between about 1.4 and 1.6 in (36 to 40 mm), though makers measure it from different places. On a bolt rifle that can be too tall for a cheek weld.
What to look for
- Offset that puts the eyepiece where your eye is, with the scope mounted on the receiver part of the rail.
- Height, and where the maker measures it from. Makers do not agree: some give the ring center above the rail, some leave the reference unstated.
- Ring size that matches your scope’s tube.
How we use it on this site
Mount pages give the offset and height exactly as the maker publishes them, with the maker’s own words for where the height is measured.