Miller Crow Foot Wrenches and Info Wanted

[Bus]

Have these four Miller Crow Foot Wrenches and would like to know how many other sizes were sold and also acquire the ones I don't have. The No. 7 is 7-1/2" inches long and the No. 12 is 14" long. Found the listing below in a 1913 Chilton Auto Directory.

[mvwcnews]

"Bus,"
A MILLER CROW FOOT No. 6 with 7/16" & 1/2"  openings (6.5" overall length)  sold on eBay in 2002.  A MILLER CROW FOOT NO. 10 is shown on pg. 8 of the Dec. 2001 MVWC Newsletter.  Its overall length is about 11.5" and the distance between the "heads" is just over 10 inches.  That hints that the numbering relates to the shank length somehow. 

[Bus]

That hints that the numbering relates to the shank length somehow. 

Stan thanks for the input. If the number does equal the distance between heads the No. 5 is probably the smallest.