The Windtech clamp for sure has a 5/8"-27 male thread. But I believe the extension pole has a female 5/8" stud, i.e. it's lacking threads. You would need an adapter to convert the clamp's 5/8"-27 male thread to a 5/8" male stud (unthreaded).
But bhadella is right -- the SuperClamp is a much better match with the extension pole. And I believe the standard stud included with the SuperClamp is a dual 5/8" male stud with a 1/4"-20 tip. So it would work with the extension pole, or with adapter(s) would also work for a standard 5/8"-27 female threaded mount.