Some years ago, I bought a plastic version of what you are describing that used Velcro to attach it to the machine. It was about an inch or an inch and a quarter in size, square, with two arms that slid along the sides to the size and type of needle. Eventually the arms broke off. It was fine while it worked, but now I just use a post it if I need to remember! I think I found it at Joann's, perhaps in the quilting notions section. HTH.