@Samuelandre it can work between smaller coin till the 2.5 centimeters , meaning 2.4cm is ok . You don't need a gimmicked coin , you need that the coin be Ferrum and not 100% silver, in my country most of the coins are Ferrum and works well with the trick, so I can borrow the coin from the spectator, if your coins doesn't attract to magnet you could convert coins at your local change currency store , or just find a coin store and ask them for specific cheap coin instead of purchasing 30$ coin . Or you could prepare at home a sticker with a thin magnet ( stick a thin magnet between two stickers ) then you stick it on any borrowed coin and ask the audience to sign it , at the end of the trick get the sticker off the coin , return the borrowed coin, and put the stickers in your pocket so you could later take off the thin magnet.
