The stem should be a standard 1" quill stem (these are 22.2mm). Some older bikes, but not many (mostly Schwinn's), as well as BMX bikes, use 21.1mm stems and those are MUCH harder to find in configurations that are like what you are probably wanting.
I bought this Kalloy stem for my Takara only to find out that I needed one of those smaller 21.1mm stems.. but it does fit in my Nishiki just fine (and may end up being used on another build.. which it seems is where most of the parts intended for the Takara are heading..).