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Airsoft 20 mm RIS and RIS II rail

The standard airsoft mounting rail: Picatinny-pattern so it takes real optic mounts, with the tolerance caveat on budget replicas.

Rail cross-section, not to scale
DesignationPicatinny-pattern, watch clones
Rail standard
Pattern
20 mm Picatinny / Weaver style, squared slots
Accepts
real Picatinny optic mounts and rings
Also called
RIS, RAS, RIS II
Caveat
budget clone rails can run out of Picatinny tolerance
Seats on it
Aimpoint Micro mounts1 inch rings30 mm ringsPicatinny red-dot risers

An airsoft 20 mm RIS or RIS II rail is built to the Picatinny pattern with squared slots, so genuine Picatinny scope rings, red-dot mounts and risers fit a good-quality replica rail directly.

The weak point is tolerance. A budget cast rail can run its slots slightly wide, narrow or off-pitch, so a mount that indexes on the recoil slot may sit loose or refuse to seat. Check the fit dry before torquing.

Metal upper receivers and quality CNC RIS II rails hold spec best. If a mount rocks, the rail, not the mount, is usually out of tolerance.

Mounts for a 20 mm airsoft rail
Search Amazon for Picatinny red dot mount for airsoftaffiliate searchFind Picatinny red dot mount for airsoft on eBayaffiliateSearch Amazon for Picatinny scope rings 30 mmaffiliate searchFind Picatinny scope rings 30 mm on eBayaffiliateSearch Amazon for Picatinny riser mountaffiliate searchFind Picatinny riser mount on eBayaffiliate
Fit an optic to this rail

Sources: 20mm Picatinny RIS/RAS rail systems, Patrol Base · MIL-STD-1913 Picatinny rail dimensions, Wikipedia