The George Barnsley Double Iron is a very popular tool, it is used in shoemaking when setting sole edges
 
The Double Iron is a handcrafted edge iron that has a double lip on the top and a single lip on the bottom which is smooth and domed inbetween
 
The Double Iron is finished with a traditional square shoemakers beech handle
 
Available in sizes A-G
Working distances
A - 1/8" 
B - 1/6"
C - 3/16"
D - 1/4"
E - 5/16"
F - 3/8"
G - 5/12"
 
See below for bar sizing;
A - 6 x 6mm
B - 7 x 7mm
C - 8 x 10mm
D - 12 x 12mm
E - 14 x 16mm
F - 16 x 16mm
G - 17 x 17mm