Answer
Rule of thumb: jap stuff uses 10mm 12mm 14mm 17mmeuro uses 10mm 13mm 15mm 17mmamerican uses 10mm 13mm 14mm 15mm 16mm 17mm 18mmthread size: 10mm head is a 6mm bolt: thread pitch 1.0012 and 13 mm head size is an 8 mm bolt: pitch 1.2514 mm and 15 mm head size is a 10mm bolt: 1.25 thread jap, 1.00 or 1.50 american and euro12 mm can be 1.00, 1.25 (jap, some american fine thread), or 1.50 (american, euro)