The first pic. from bottom to top. 1928, 1930, and 1931. The 28 is much thinner, shaft is 9/16 and handle is 25/32, the 30 the shaft is 5/8 and handle is 7/8 on the 31 the shaft is 5/8 and handle is 15/16 . where the handle meets the shaft is different on all three. The width of the head is 15/16 on the 28 and 1-1/8 on the 30 and 31, The hole for the bar is 3/8 in the 28 and 7/16 in the 30/31. and in the 31 its located further down the handle.
Second pic. on the 28 and 30 "Patent applied for" is stamped on the top end of the shaft. Also the 28 and 30 have a hole in at the end of the shaft, the head had a special locking device which held it into position. This may have changed in the 31. Also the 28 the socket holder is cut square with the length of the shaft, and in the 30 and 31 has a 45 degree offset.
Third pic. The 31 has a female slot at the end of the handle.
Later the model numbers for the 15" were changed to like 10-D 10-DA NS-15, the hard part to get with these are the bar that fits into the handle hole.
