The International Organization for Standardization (ISO). First edition. 2007-12-01. 10p. This part of ISO 6360 specifies the code numbers for specific characteristics of root-canal instruments. This three digit number appears in the locations 10 to 12 of the 15-digit overall number and forms the fourth group of three digits in the 15-digit overall number, the principles of which are explained in ISO 6360-1 and ISO 6360-2.