I've heard many times that just about all pre WWII balloon tire bicycles use the same stem size- 7/8". Is this true?

I've located a nice set of crosspiece handlebars with stem for my Schwinn, but the stem appears to be made by "Rollfast". Both are from the same era- mid 1930s. Would a Rollfast stem work with a Schwinn from that same era (that is to say they both would have taken a 7/8" stem)?

(cross posted to mechanics too)

Any help is appreciated.