Rob Allen Whitetip Snorkel Size:OS Its universal cross slot design accommodates Size:1m Its universal cross slot design accommodates both picatinny and weaver style rings Superior Visual Performance: These scopes deliver stunning visual performance This semi rigid flexible design also helps with divers who wish to chase crayfish as it stops the snorkel from becoming a snagging hazard in overhead cave environments The softer semi rigid design of the snorkel bore also increases the streamlined hydrodynamic design of the snorkel in the water and eliminates that annoying banging against your head characteristic that similar products are renowned for