The pressure type bolt elongation measuring ruler (hereinafter referred to as the measuring ruler) is a specialized measuring tool used to compare and measure the length of steam turbine cylinder bolts before and after hot tightening.The characteristic of our company's research and development of a pressure type bolt measuring ruler is that when measuring the length of the same bolt before and after hot tightening, the pressure of the measuring ruler's pressure plate is consistent with each time it hooks the bolt under the action of the pressure spring. Therefore, the comparison measurement of bolt elongation before and after hot tightening is more accurate.