I think it about 30 thou between coils or double up a match book. Those 2 prings have a force of 620 lbs at the 30 thou. I was blown away how strong they are. I was cheap in a pinch for time and got some from the hardware store and had the same gauge and tension it seemed, but only had 230 lbs.. I fought the pipe blowing all season 2 years ago and finally got out my spring tester at it was obvious why my pipe was lifting and donut was rotating causing a big boost leak. All of the stuff the springs mount to flexes too so the spring has to have a big enough range to keep it tight even with the flex.