The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com  A New Form Of Compact Induction Coil 9" x 1.5" Core; 4 turn Primary (5/8" wide ribbon), 2.375" OD x 6" Secondary, wound with 34 AWG wire for 4.375" length - single layer. Sparks up to 2.5" long so far... Click here for a movie!