The TrustFire X8 is the most recommended light source for GuerillaBeam projectors. This adapter creates a very strong connection to the flashlight. It's easy to print too. See https://gbeam.de/products/adapter-for-trustfire-x8-flashlights/ for additional details. Update 2015-05-16: New revision 4 Improved fit and printability. Increased length to reduce creep when hot. Also reduced the stress on the 'hinges' for easier assemby with less danger of inadvertently breaking the adapter.