This is one of those accessories that is a "jack of all trades" type of adapter. It consists of two baby 5/8" (16mm receivers) on either end joined by a tilting pivot and a ratcheted metal handle to lock it securely in place and a hole with a set-screw to lock an umbrella shaft in place.
This adapter enables you to use an umbrella with light fixtures that don't have a place to accept an umbrella shaft.
Two 5/8" (16m) studs accompany this adapter. The KG000912 has both 1/4"-20 & 3/8"-16 male threads on either side and the KG001112 is tapped with 1/4"-20 & 3/8"-16 female threads on either side.