Pressure of 400 pounds ( 180 kg ) on the center of the mine or 200 pounds ( 90 kg ) on its edge deforms the pressure plate compressing a spring, and breaking a shear pin which holds back the spring-loaded TNT . Most were painted field gray ( dark green ).
42.
In 1848 Lewis Temple, an African-American blacksmith in New Bedford, Massachusetts adapted the toggling harpoon using a wooden shear pin to initially brace the toggle head, and created what came to be known as " Temple's Toggle " and later simply as the " toggle iron " or " iron toggle " harpoon.
