The BBClip uses a ball bearing and gravity to gently hold onto thin flat material like fabric, paper, etc. With the magnet you can conveniently place it near where you are working and need things handy; it's great for increasing your work surface area by keeping papers off the horizontal surface.
There are two version available. One uses a 10mm ball bearing and the other is sized down to use a 9.5mm (3/8") ball bearing. Both version have a hole in the back that is 8.2 mm diameter x 3.2mm deep. I found that this made the hole tight for a standard 8mm dia x 3mm neodymium magnet. Simply press the magnet in using a good amount of force and it won't come out again - no need to use glue!
See the video for a demo of how to assemble and use. https://www.youtube.com/watch?v=0p33Bq12Xrs