Black leather slip-on shoes size 7.5

Black leather slip-on shoes, have kind of thick nubby soles the only markings on them are on the hill and say 40 250. So I don't know if this is European sizing or what. Be there in really good condition there's no wear or tear on the upper leather part. I just can't find any markings. I'm guessing them to be a seven and a half because that's what I wear and they feel a little wide but my toe goes to the end.