B0N3You can use a 3mm x 23mm tritium vial, but it needs to be mounted in an adapter. We have a DIY kit on our site that includes materials for 2 adapters, but they are essentially clear acrylic tubes with some extra o-rings and washers. Some vendors that sell tritium also sell completed "modules" that have the tritium already mounted in the adapters. This way you can just exchanve the Embrite glow pellet for the adapter