Vise screw threads

We were discusing Acme threads yesterday and began by looking at several vises. Most were very straightforward, but the Kurt model D60 has the screw inside some sort of cover. SO naturaly I counted the turns of the handle while measuring the jaw opening. WHA!!!! It came out something like 1 1/8 inches/10 turns (not exactly) so I says to self, maybe it's metric. HA!! It comes out something close to 3.6mm pitch. Thats not in amy list of threads I can find. Up in that range all I see is 3 3.5 4 mm . So does anyone know what gives with the screw in that vise? ...lew...