Ruby 21 (25mm) Mech Kit by Kennedy EnterprisesKennedy's Ruby 21 is a beautiful and simplistic mech mod featuring a one piece design (mod with built in atomizer) with minimal voltage drop.  Product Features: Kennedy 25mm Ruby One Piece Design Fits 21700 and 20700 Fits 18650 With Adapter (sold separately)   Constant Contact Switch Included Completely Rebuildable Lifetime Warranty Smoother Airflow 26mm Outer Diameter 25mm Build Deck Bottom Airflow Easy to Clean Redesigned Super Smooth Constant Contact Switch (no tools required); virtually eliminates arc marks on your batteries Extremely Low Voltage Drop Due to One Piece Design ADVANCED USERS ONLY - This is a mechanical device which is only suited for users with advanced knowledge of coils, builds, and ohms law.