All 12B Krieghoff factory and titanium choke tubes are numbered as follows:
 

No: Size Diameter US Eng
 
00 0.00" .732" Cyl Cyl
0 0.05" .727" Skeet Imp Cyl
1 0.10" .722" Imp Cyl 1/4
1+ 0.15" .717" Light Mod 3/8
2 0.20" .712" Mod 1/2
2+ 0.25" .707" LIM 5/8
3 0.30" .702" Imp Mod 3/4
4 0.35" .697" Full Light Full
5 0.40" .692" S.Full Full