This is a round flange which mounts on top of the deck used for a rail or ladder with a rail outside diameter of 1-1/2", this is almost always used with above ground equipment. 

• Outside Diameter: 3-3/8" (Bottom Mounting Flange)
• Ouside Diameter: 1-3/8" (Top of Flange)
• Inside Diameter: 1-9/16" (Top Inside) 
• Height: 2-3/8" 
• Mounting Holes: 2-5/8"
• Diameter on the Bolt Ring there are a total of three holes the center to center measurement from on hole to another 2-5/16"

Includes Mounting Flange and Bolt