It is a 22 mm mouthpiece liner, fitting Free-Flow, Visi claw,F-300 claw SoffiClaw Strangko and Flo-Star Max claws with a 185 gr. stainless steel 19 mm shell.
This liner is a result of years of experience, gently milking the cows and keeping the udder healthy.
Can be also used with a special sight glass if one needs a two piece liner. (see picture)