Just to clarify my previous posting on pipe size, I when out and checked the 7 scraped mounts I have and out of the seven here what I found....I was wrong on the 4 1/2, should have been 4", but the larger size may only apply to people with the Raydex dishes.
1 Winegard 10' dish mounts use 4" OD pipe
1 Zenith 8' dish mount use 4" OD pipe ( same mount as the Winegard )
1 use a 3" OD pipe
4 used 3 1/2 OD pipe
Now both my Raydex dish are using a 4 1/2 inch OD pipe because of the way they mount to the pipe, I could probably go up to a 6" pipe with them, only being limited to the bolts length.
In your case get the dish before getting buying any pipe due to the different mounts and there requirements