Top insert for square tube. Investment cast 316 stainless. Sold per each. Tube Outer Dimension: 1.25" x 1.25" Tube Internal Dimension*: 1" x 1" Pin size: 1/4" Sea-Dog Line is a 3rd generation family company with a history of satisfied customers stretching back to the company's start in 1933. The company is the recipient of multiple industry awards for quality and efficiency.