A NATO watch strap (abbreviated at a "NATO strap") is a single piece watch strap originally designed for the British Ministry of Defence in the 1970's, made from quick drying and nylon, and very durable for use in combat situations. It also has a safety feature where if one of the spring bars pops out, the strap remains on the wearer's wrist. The NATO strap was popularised by James Bond (played by Sean Connery) in the 1964 film Goldfinger.
You can purchase a Nato strap online from Natostrapstore.com here.