When did Ford introduce the new style filler plug for the rear axle? I have a Jan.1 1927 parts book here, and it is listed in there, so could it have been used in late '26 too?
Larry, Our October'26 assembled Runabout had the new style filler plug
From the encyclopedia:
Recessed square socket pipe plug. (The change to the pipe-plug was noted in a release dated late 1925 but many of the large-drum ('26-27) housings
have the 15/16" hex screw.)
This made me curious, so I went out and looked at five large drum housings. Three have the pipe plug and two have the old style. The only one I can date, on a 7-8-26 chassis, has the new style.
One might be able to review the Ford parts catalogs and be able to verify when they remodeled the adjustable wrench - # T-1387 to have the square end on the handle to accommodate removing that pipe plug with the 3/8" square.