Shomer-Tec Hollow Spy Bolt Secret Storage Container Updated and improved version of the old Soviet KGB dead drop hollow bolt used during the Cold War Looks like an ordinary 3/4" diameter bolt (3.43" long), but hollow It has reverse threading on the bolt head for additional security Features an O-ring seal for weather-proof storage of small valuables, communications, etc. Its secret storage compartment has a diameter of .49 and a maximum depth of 2.81