This is a short stub KF-50 to 2.00 inch MALE BSPT Tapered Thread. This thread size is primarily used in Europe and Great Britain. This adapter converts BSPT tapered thread to a KF 50 flange which is more commonly used in the universal world wide vacuum market.

BSPT = British Standard Pipe Taper (tapered thread).

Adapter KF-50 to 2.00 in. Male BSPT, Stainless Steel
Flange Size: ISO-KF NW-50
Pipe Thread BSPT (British Standard Pipe Taper): 2.00 in. BSPT-Male
Common Dimensions: A = 2-15/16 inch (75mm), B = 2-3/8 inch (60mm), C = 2 inch (51mm),
D = 1-3/16 inch (30mm)