Blaine forwarded photos of a Willys Wagon with the one-lever-style Dualmatic hubs that include a center bump. I don’t have docs that conclusive identify this one-lever hub as a Dualmatic, but it seems highly probable. Given the design, an attempt to secure the lever with a bump to keep it from shifting, it is likely it was an iteration of the original Dualmatic one-lever hub.

Below is what I have documented for the one-lever Dualmatics and my related guesses as to why. (For two-lever variations of the Dualmatic hubs, try this link)

As a reminder, here is the original patent by Simonsen for the Dualmatic:

Here’s what I believe that original hub looked like:

This was likely the second version, this time with two circular bumps:

One of the issues with both of the early versions was that the internal forces apparently could cause the lever to bend. Here’s an example:

To halt that from happening, as photographed by Blaine on a Willys wagon, Dualmatic may have gone with this design:

A similar design was photographed on a Dodge truck (or I was told it was a Dodge truck):

Perhaps Dualmatic concluded that the simple one lever design simply didn’t hold up, so the company shifted to a two lever design. This is the point where it would be good to compare the internals of the one-lever vs. two-lever design.