Make a square material into a circle

I am trying to make a sniper scope for an FPS shooter and have used a

tied to a

which is used as the Texture for a

which is used as a

. The trouble I’m having is getting it to show as a circle instead of the full square. I imagine this would be accomplished using either a SphereMask or SphereGradient in the Material, but I cannot get it to work. Or could this be accomplished in a different way, such as via UMG?

RadialGradientExponential connected to opacity on a translucent material

Thanks. This worked perfectly.