Yes, they describe the various chokes.
* Full *- Improved Modified ** Modified **- Improved Cylinder **$ Skeet *** Cylinder Bore
Modified.
By opening up or constricting.
FullF0 (*) ISP(¹).Improved ModifieldIM00 (**) IISP(¹).ModifieldM000 (***) IIISP.Improved CylinderIC0000 (****) IIIISP.CylinderCLC0000 (C****) IIIIISP.Skeet(2)SKSK (Skeet Beretta)No NotchesSP
Chokes for shotguns shrink the bore's diameter to tighten the shot pattern and increase practical range.
they help with patterns of shot and accuracy of slugs
A good basic article on chokes http://www.ssaa.org.au/stories/shotguns-a-beginners-guide-to-shotgun-chokes.html
Try e-gunparts.com
Refers to the amount of constriction at the muzzle.
Herter's sold various maker's products with their name on them.
Yes chokes are designed to tighten shot patterns.