The heavier the better obviously, I made mine with 15% infill and 3 walls, no supports required for print. For the string I used the $6 250 foot green string from Walmart. After you route one end through tie about 3 stacking overhand knots and pull in until it gets jammed, and you can pull whichever way to get it centered correctly. Depending on application adjust how long you want your string to be. I’m using this one for ADAS Calibrations for vehicles at work, so roughly 5ish feet will work perfect for me!