Narrow crown, relatively heavy gage, like used in cabinet shops for putting things like thin plywood backs and skirts on. I've got 2 or 3 of them, old (really old) Bostich, Duofast, maybe an import. Hard to dig through the shelves sometimes.
Shoot staples from 1/2" to about 1-1/2" long. (maybe longer, these days)
Crown is about 1/4" to outside of legs. (IME it can vary a tiny bit between brands, or did in the old daze. IOW, check carefully if buying one brand staples for a different brand gun. Most mix-n-match, some in the past did not.
Just google: narrow crown stapler & read the reviews & price options.
smt
Sorry - Geoff types faster than me and is more to the point!