Speks 2.5mm magnet balls were designed with safety in mind. While most brands of magnet ball sets are 5mm in diameter, Speks are half of that size. Because of this, the magnetic flux index (a fancy way of measuring strength) is less than 50 kG2 mm2. This is many orders of magnitude below other magnet sets containing magnets with a magnetic flux index of 300-500 kg²mm² that have caused intestinal perforations in the past. Specifically, accredited 3rd party tests of Speks 2.5mm magnets report a flux index of between 20-35 kg²mm².