It accepts a 2" OD mast - I can't comment on the stability of an adapter; I'm sure that depends on location and potential wind load.
Thanks for the response. An adpater would be a temporary solution. Too cold for me in January to dig a 3 foot hole and pour concrete. Solid Signal has one 12 inches in length.
12 Inch Pipe Adaptor Converters 1.65" to 2" Outer Diameter Wild Blue Compatible - Skywalker - SKY1101 -=