3500 psi HP100 or 3442 psi? Different neck threads, different valves....They most definitely DO exist. My doubles Are HP 100's and had a "pro valve" manifold when I first got them. I replaced it with a Thermo manifold once I finally tracked one down lol. Only time I ever used an insert was when I was transfilling with a scuba to paintball tank adapter... MAY have some pictures somewhere still of it if interested in checking it out...