Calumet MF6830 Swivel Universal Umbrella Adapter The swivel umbrella adapter provides a 5/8 female mount both top and bottom. One adapter with 1/4-20 and 3/8 male threads and one with 1/4-20 and 3/8 female threads. A locking receptacle that will hold umbrella shafts up to nearly 1/2 (12mm) diameter.