20mm vs 22mm rail?

[mactroneng]

I've got a new purchase coming and I'm looking at cheap reflex/red dot sights on Amazon. Most of them say they fit either picatinny or weaver rails but then they say they fit either 22mm (most of them) or 20mm rails (a few of them) and I can't find any info about this measurement anywhere. What does it mean?

Thanks

 

[Evanguy]

It is the width of the rail. Pellet guns and 22's can have down to 9.5mm or 11mm

So if your to narrow or wide you cant fit the mount or it won't be able to tighten up. You need to know your rail width.

 

[Hitzy]

Picatinny rings/mounts will only fit on picatinny rails, Weaver rings/mounts will fit both. It's the width of the recoil lug on the mount that is different thickness, picatinny being thicker...too thick for Weaver cross slots.

 

[Blastattack]

Picatinny rings/mounts will only fit on Picatinny rails, Weaver rings/mounts will fit both. It's the width of the recoil lug on the mount that is different thickness, Picatinny being thicker...too thick for Weaver cross slots.

Essentially, there is no such thing as a 20mm or 22mm rail. Both Picatinny and Weaver share the same profile dimensions, but as stated the shape and width of the recoil grooves differ.