RAM® 方形立柱夾具底座（適用於寬度達5英吋的立柱） - D尺寸

Installed this on a wooden post at my dock and the ball mount feels rock solid. The clamp tightened evenly around the 4x4 without any slipping.

Finally found a clamp that actually fits my 4-inch wooden posts without any shims or adapters. The stainless steel hardware feels really solid and should hold up well to the weather.

The 2.25" ball connects perfectly with my existing D size arm, and the clamp grips my 5-inch post without any wobble even on bumpy roads. I was worried about install time, but it took under ten minutes with basic tools.