They fit like a glove too. @Mark@LF has built some mighty fine modules for the X3 that were once thought to be permanently stuck in a drawer after the factory bulb blew.
My K2 porcupine is now not only capable of collecting DNA samples, but now it can blind a perp at 25 yards.
Pentagonlight had made a tremendous amount of flashlights before that took place. Mark decided to make some modules spec'd for them. The X3 had an oddball size module that many wanted to upgrade but there were no options available until now. Same with the K2 porcupine and X1.
Member Lightknot had 7 LED modules built for the X3. After that, there were no other options. I bought 2, he kept 2 so there were only 3 in the wild somewhere. An M31 was an option for the X1. There were no options for the K2.
Mark chose the 519 LED for the modules. Plenty of throw, plenty of spill.