F-series logo and style progression

Extensions
The style of the extensions changed, but the listings really do not reflect this.  Shown in the top picture is a full set of extensions with WWII.  Most are not date stamped, but they still can be dated. The next 2 photos show the heads and the logo differences.  The earliest extension heads are un marked (these have labels on the shafts). The late 1930s (1937?) changed the head style through 1948. The FX heads have 2 ribs and are 1948 – 1978?

The FX-20 ran through 1935 – 1953 and changed heads through the life of the tool.

The 3rd photo from the top shows the same order of the squares. There is a noticeable rib in the earliest example and random variation after this. The last one is different. It is an industrial extension and does not have a friction ball, but a rod. This “locks” the socket in place and is not change friendly (But locks the socket on for tight areas). 

The last photo shows 3 logos of the early (pre 1937) extensions. We know these are all post 1933 and pre 1937.. I don’t know the correct order.