The Back to Basics V4 Knurled by Purge Mods is a competition winning mod and is a different animal this time around as it uses the 21700 batteries instead of 18650 batteries. The button housing is comprised of 3 very strong magnets which ensure a comfortable throw and one hell of a hit and one beefy copper contact pin. The threading on each mod is flawless and they are weighty too, these mods ooze high-end quality. This mod comes with a rugged, hard shell carry case.