Spinnaker Pole Ring

[PA412]

Hi all,

Looking to fit a spinnaker pole ring on the front of my mast for running a pole downwind...anyone know what the mast radius is? I see alot of fittings for sale that have a 2 inch radius but I'm thinking that's a bit big. Something like this?

http://www.apsltd.com/spin-pole-mast-ring-1.html