About 20mm Picatinny RIS/RAS Rail Systems

20mm Picatinny rails, also known as "RIS rails" or "RAS rails" is the current most prominent attachment interface found on Airsoft guns and allow all manner of accessories to be mounted, including red dot sights, scopes, vertical foregrips, iron sights, laser aiming modules and tactical flashlights

The Picatinny rail, also known as a "Pic rail", is a development of the earlier Weaver rail with tighter tolerances, some dimensional changes and squared-off slots between each "tooth" of the rail. Accessories for Weaver rails can generally be mounted onto Picatinny rails, but the reverse is not true unless the Weaver rail is modified. 

The benefit of 20mm Picatinny rails is its absolutely massive range of accessories, offering everything from vertical and angled grips to grenade launchers, bipods, PEQ lasers and rail covers which can be mounted wherever there is space. 20mm Picatinny is also far easier to master than the more modern M-LOK and KeyMod, with easier and quicker mounting interfaces and the ability to quickly change configurations with minimal effort. 

Following its adoption by the US military, the Picatinny rail became the standard for Western militaries and is now found on almost every modern rifle in service, as well as on the frames of many modern handguns.