I am not happy with the valve stem attachment, there are threads in the air cartridge and they do not fit well into the air column. Probably the worst design I've ever seen, it either crosses the threads or doesn't stay on the valve stem. I can't believe Milton invented something this shitty. I've seen cheap Chinese cartridges that are way better than these and what I'll probably do is back one of those cheap cartridges and throw the Milton in the trash. The rest of the device is fantastic, but whoever designed this should be fired immediately.