Thread Reel with Caps by Top Shelf Magic.
Thread Reel is an invisible thread reel that gives you useable length of invisible thread in a compact unit that can be concealed anywhere. While the thread is invisible, you can instantly gain access to it by merely grabbing the wax ball, and moving out from the reel to an object such as a table edge, deck of cards, or book as an anchor.
The Thread Reel clips under the jacket collar, inside the edge of the shirt, or top of the shirt pocket, anywhere that the thread will have a non-restricted path feeding out of the reel to the anchor point. The end of the thread is attached to the wax ball that is pressed to its side. Merely pull the wax ball free of the Thread Reel and move it out from the body and press it to the anchor point and you will be left with a line of invisible thread running from the reel to the anchor point.
The Thread Reel thread, while being invisible, is very strong for its thinness, but do be careful not to break it with quick jerky motions or by trying to put too much strain on it.
Thread Reel with Caps by Top Shelf Magic