That is just 3/4 galvanised pipe. The thread in the puck base is 3/4"X14 thread which is the same as a 3/4" pipe thread. It would not start because the pipe thread is tapered so i took a 3/4 pipe tap & some wd 40 & gently cut the threads in the adapter a little deeper. Just be careful & only go about a round at a time with the tap & then clean the abs plastic from the threads. It took about 15 minutes to cut the threads out, just be careful & don't get in a hurry & put too much pressure on the base as it could split. If you don't have a tap just about any plumber or machine shop will have one or you can buy one for about $10.00-$15.00 at Lowes or home depot.

I am planning to make a hinge to where the mast will fold down to the back of the boat to be out of the way for storage.

I feel that having the GPS puck up above the top for a 360 degree view of the sky is the seceret to good GPS performance