The Spy Bolt is an updated and improved version of the old Soviet KGB "dead drop" hollow bolt used during the Cold War. It features an O-ring seal for weather-proof storage of small valuables, communications, etc. Simple, ingenious design is essential for the concealable gadgets spy work calls for. The Spy Bolt fits the bill perfectly. This device utilizes a ½" diameter bolt providing a larger storage area than the original. It also features reverse threading on the bolt head for additional security. BONUS only in 4.8 cubic inch bolt: The larger, 4.8 cubic inch bolt now comes with 2 storage containers that fit neatly inside of the bolt. Use is optional, but these containers can come in handy if you'd like to keep more than one item separate within the bolt. The containers feature a water tight plastic screw top and durable glass transparent body. Capacity of each container is 4mL.