This package of eight large magnetic closures is from 49 and Market. These are neodymium magnets that measure 15 mm x 0.8 mm. These are ultra-thin magnets with a strong magnetic pull and can be used for interactive elements on your craft projects. 
Note: This is a warning from the manufacturer: Use with extreme care. Neodymium magnets are strong, brittle magnets that need to be handled with care to avoid injury. Keep away from children, for adult use only. Strong magnets may be harmful to pacemakers.