Write Size Pen by Jon Allan

Size Matters The magician hands out a "mini-pen," about half the length of a normal pen and explains that there are ways to make it bigger. One is with a magnifying glass; the other is to stretch it. Holding the pen between his hands, the magician starts to visibly stretch the pen until it's the normal size! The pen may then be handed out for examination. Comes complete with normal pen, mini pen, magnifying glass and detailed instructions.