Choke Tube History:
 The current system of screw in chokes was introduced in 1959 by winchester with its model 59 semi-automatic shotgun. They discontinued the model 59 in 1965 to make way for their new line of shotguns model 1400 semi-automatic and the model 1200 pump and they were introduced as fixed choke guns, it wasn't until around 1970 they had worked out some problems with their screw in choke system they then offered this in the 1400 and 1200 model shotguns they named their new choke system winchoke.
 In 1978 the mossberg 500 was first seen sporting the new choke tube system they named their new choke system accuchoke.
 In 1982 weatherby introduced the model 82 with the new screw in choke system they named their new choke system multichoke.

 All The Above Systems Were Interchangeable:
 After this, all the shotgun manufacturers introduced their own versions and systems of screw in choke tubes.

 Choke Tube Selection:
 This is really a confusing issue amongst a lot of shotgunners but one that is easily explained. Everyone knows how to pattern a shotgun and what they are looking for, which is the ultimate full choke pattern at 40 yards it is this area where it all gets fuzzy and needs explaining.

 Why Full Choke Pattern:
 The reason for placing 70% of the shot in a 30" circle at 40 yards for a full choke is this, the minimum - maximum pattern kill zone, this means the pattern will cleanly kill anything in this circular zone.

 Choke Selection:
 Selecting a choke tube is nothing more than moving that same exact pattern to different yardages in other words if you want to shoot at a target 20 yards away then select a choke that gives you 70% of the pattern in a 30" circle at 20 yards, if shooting at a target that is 45 yards away then select a choke that will give you 70% of the pattern in a 30" circle at 45 yards.

 Which Choke Delivers 70% Pattern At Given Yardage:
Extra Full - 45 yards.
Full - 40 yards.
Modified - 35 yards.
Improved Cylinder - 30 yards.
Cylinder - 25 Yards.

 Rather Simple Don't You Think:
 With most sport hunting and competition built guns the manufacturer will make choke tubes that will accomplish this pattern at several different yardages that have known yardages in their respective shotgun sport.

 Buying Choke Tubes Online: Choke Tubes

 After Market Choke Tube Manufacturers:
Briley
Carlsons
Colonial Arms
Comp-N-Choke
Hastings
Trulock
Wad Wizard

 Choke Tube Thread Specifications: