A metal O-ring is provided. The metal O-ring has a sidewall with an outer surface and an inner surface. The outer surface of the sidewall is machined to selectively thinning the thickness of the sidewall, such that the sidewall of the of the metal O-ring has a plurality of thicknesses equal to or less than a maximum thickness and equal to or more than a minimum thickness. Selectively thinning the sidewall by machining the outer surface allows for control of the elasticity of the metal O-ring. Controlling the elasticity of the metal O-ring, and potentially increasing the spring back, may provide for increased contract pressure at a sealing interface, which would facilitate sealing. The machined outer surface of the metal O-ring are generally machined to flat surfaces.