The Best Way to Carry a Paddle
I've only used it to carry a paddle, but a windsurfing mast should be perfectly fine.
I'm using them on Thule Rapid Aero load bars, mounted out at the otherwise unused ends of the bars.
Rubber padding is just the right density and softness to work well but not mar what you're carrying. Ingenious design makes it simple and quick to use. Not noisy at speed.