3.4 cm / 1.3 inch edge
This of cause is just a home made Tetraminx. I remember seeing it on a single sheet advert many years ago, long before it was ever mass produced or named Tetraminx. I couldn't buy one so simply made one for myself in the eighties. You can now by factory made versions from Uwe Meffert. Just click on the shop below and select "Meffert's Puzzle".