"I can't say I disagree. The term "plate" was initially used in wood car construction, so there was little confusion with "plate" steel.
Also the member across the bottom of car framing is almost universally called a "sill" (side sill, end sill) because in invariably spreads the load and transmits it to the bolsters. This differs from common architectural usage, where the "sole plate" of a stud wall, for instance, serves to space the studs, but doesn't actually distribute their load, and so isn't actually a sill, and therefore isn't called a sill."
ARA Plate 305 (circa 1930) is titled: END PLATE. The revised 1930 drawing is a pressed 5/16" member with the first leg being 3 1/8" high, inward section 5" in depth and an upper leg 8 1/4" high. The upper leg is cut to the pitch of the roof.
"Now that we're through the definition of "plate", the distinctive feature of the piece that both CV and CN used is that it's a steel pressing, rather than a length of standard section structural steel."
I am not sure if a standard section was ever utilized for this particular member, at least not within the ARA designs. Flat plate was pressed into the "Z". The drawing called out for a 5/16" radius at each of the two bends. Any other member utilizing a standard section is called out as such.
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