Could have been a broken push pin - one of these:
http://www.amazon.com/Clear-Magnetic-Push-Pins-Whiteboards/dp/B0168YC5OA/ref=sr_1_27?s=office-products&ie=UTF8&qid=1462763985&sr=1-27-spons&keywords=magnetic+glass&psc=1 From: H Ucar I hope these links to pictures of the item will work. https://goo.gl/photos/nPhqELc8WufQMen2A https://goo.gl/photos/oHn3eETYbzmPfpvx6 https://goo.gl/photos/71g3uqYPpddQAShv7
