Final answer:
The 5th and 6th positions of a National Item Identification Number (NIIN) are called the Material Type, which specifies the Federal Supply Class (FSC) of the item.
Step-by-step explanation:
The 5th and 6th positions of a National Item Identification Number (NIIN) within the context of the NATO Coding System are referred to as the Material Type. A NIIN is a nine-digit numeric code which identifies each 'stock listed' item of supply. The first two digits are the National Codification Bureau (NCB) Code, which signifies the country coding the item and the next seven digits are the unique item identification number. Specifically, the 5th and 6th positions within the NIIN denote the Federal Supply Class or FSC, which classifies the item by the type of material or service it represents. Options provided such as Part Number, Location Code, and Revision Number are not correct for the designation of the 5th and 6th positions in a NIIN.