 The bomb was made of metal that could have come from a home workshop . The primary component was a piece of metal pipe , about 1 inch ( 25 mm ) in diameter and 9 inches ( 230 mm ) long . The bomb contained smokeless explosive powders , and the box and the plugs that sealed the pipe ends were handcrafted from wood . In comparison , most pipe bombs usually use threaded metal ends sold in many hardware stores . Wooden ends lack the strength to allow significant pressure to build within the pipe , explaining why the bomb did not cause severe damage . The primitive trigger device that the bomb employed was a nail , tensioned by rubber bands designed to slam into six common match heads when the box was opened . The match heads would burst into flame and ignite the explosive powders . When the trigger hit the match heads , only three ignited . A more efficient technique , later employed by Kaczynski , was to use batteries and heat filament wire to ignite the explosives faster and more effectively . 
