From the Remington web site:
Question
What are the diameters of the 12 ga. turkey chokes?
Answer
The 12 gauge Turkey RemChokes have the following diameters:
Turkey Super Full 0.665 (+/- 0.001)
Turkey Extra Full 0.687 (+/- 0.001)
Hevi Shot 0.675 (+/- 0.001)
Ventilator 0.655 (+/- 0.001)
Turkey choke tubes labeled for "lead only" are not intended for use with steel, Wingmaster HD or Hevi-Shot shot. The Hevi-Shot choke is capable of handling Hevi-Shot, Wingmaster HD, steel, or lead, however has the optimal constriction for patterning Hevi-Shot for the tight patterns needed for turkey hunting.
