5ive Star Gear Spy Bolt Hidden Safe. An updated and improved version of the old Soviet KGB "dead drop" hollow bolt used during the Cold War. Features an O-ring seal for weather-proof storage of small valuables, communications, etc. Reverse threading on bolt head for additional security. Utilizes a 3.43" long, 3/4" diameter bolt providing a large secret storage compartment with a diameter of .49" and a maximum depth of 2.81".