All S-12s except the 4th that is a SX-12.
top photo 1927 and 1928 square shafts
2nd extension 1930s until 1935/6.
3rd style started 1937 to 1946/7.
4th head style post 1948
These are all S-12s except the 4th that is a SX-12. On the top photo I have two examples date marked 1927 and 1928. The only period where square shafts are used are from this period 1920s until 1930 or so. The 2nd extension is from the 1930s until 1935/6. These have blank heads and the lable is on the shaft. The Logo is large with a larger S and the up turned dash. The 3rd from the top this style started is 1937 and lasted until 1946/7. These have the knurled head seen is many WWII period tools. The 4th extension has a head style from 1948 and lasted past 1970.