20 gauge Rizzini chokes. Twenty gauge barrels come in two bore profiles — Plus and standard Rizzini — and each is threaded and bored differently, so the profile has to match the barrel. Plus-bore guns take flush tubes in seven constrictions or extended tubes in six; standard-bore guns take flush tubes in six.
Flush tubes sit level with the muzzle; extended tubes stand proud and are knurled so you can change them by hand between stands. Nominal bore is .615″ (15.6 mm).
