Russian MP-153, MP-155, MP-27, MP-18 caliber 12 Baikal barrel extension multi choke with muzzle brake grooves. Length 130 mm. Weight 125 grams.
white-green dots – cylinder ( 0.0 mm)
white-yellow dots – half choke (0.5 mm)
white-red dots – full choke (1.0 mm)
You may also use semipositions (between dots). You will have 0.25 and 0.75 choke.