This is a Wilson Combat known as the Recoil Spring, model 10G18.
Wilson Combat Heavy-Duty Recoil Springs are made combat tough to repeatedly take a pounding yet show remarkably consistent performance every time a round is fired. Keeping a fresh recoil spring in your pistol will dramatically reduce the pounding your slide and frame receive.
Features:
2,000 Round Average Service Life
Heavy Duty
Reduces Wear on Slide and Frame