What is "triphammer"

Usage examples of "triphammer".

And from inside the mill came not the harsh grinding of the corn-mill but the continuous Iblis-clash of a triphammer forging iron.

But the guidance came not from Nicolson but in the shape of a crescendoing roar of an aircraft engine, the triphammer thudding of aircraft cannon and a shell that screamed through the smashed window above their heads and blasted the top of the chartroom door off its hinges.