Pack of 2 Double-Sided Go/Stop Magnets Diameter 50 mm : Amazon.co.uk: Stationery & Office Supplies
XFasten Magnetic Tape Strip Roll, 1/2-Inch x 10-Foot (50.8mm x 3.04m), Self-Adhesive, Peel and Stick on Double-Sided Magnet Strips for Fridge, Crafts and DIY Projects : Amazon.co.uk: DIY & Tools
electromagnetism - Why does the side of two magnet attract? - Physics Stack Exchange