My tightest skeet choke .410-bore is my pre-war Model 42 with .006". Other skeet .410-bore barrels I have are .002" (2), .004" (2) and .005". My .410-bore spade for my bore mic won't go in the full choke barrel of my Winchester Model 23 Classic, but I finally ran into one that would and that choke is .028". The Ithaca Gun Co. Standard Bore, Chamber & Choke for Shotguns drawing and tables gives .020" for a .410-bore full choke, but my NID has .024".