CAD designed and built to Aerospace specifications from chrome silicon, corrosion resistant, stainless steel or chrome vanadium for maximum durability, consistency and reliable performance. Built to aerospace specifications; heat treated, shot peened and fully stress relieved to minimize spring set. 1911 AUTO MAINSPRING - Stainless steel (SS) or chrome silicon (CS); wound in the very popular 19 lb. and 17 lb. rate for lighter, consistent trigger pull with reliable ignition. Mfg: Ismi SPECS: Chrome silicon or stainless steel round wire, chrome vanadium flat wire.