Summer a few years back I bought a weird looking plane whilst on holidays in the Finger Lakes, NY. It doesn’t have many markings, which makes it one of the most challenging planes to identify. It is a No. 04 smoothing plane with an iron body, aluminum lever cap, hardwood handles. It is 9″ in length, and 2″ in width, and has “P4” marked on the body behind the frog.
It seems to be based on US Patent# 1,914,609, Filed Feb.19, 1932, received June 20, 1933.
The patent shows a circular knurled knob, whereas this plane has the knob which is more of a curvilinear square. This knob has three characters, H, K, and 1 stamped on it.
Both the plane body and the lever cap have “PAT PDG”. Actual planes made after the patent have lever caps made of steel.