BibBits Magnetic Race Bib Holders (Safety Pin Design) Dimensions: 20 x 15 mm Total Weight: 20 grams BibBits are not a toy! Keep away from children. Keep BibBits away from all devices that can be damaged or influenced by magnetic fields like bank cards, credit cards etc. BibBits can influence the working of pacemakers etc. People using such devices cannot use BibBits. When you wear a number bib with chip, please put BibBits beside the chip. Normal use of BibBits will normally not influence the working of heart rate monitors or timing tags, but always test this before using.