This is a short stub KF-40 to 1.25 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 40 flange which is more commonly used in the universal world wide vacuum market.

BSPT = British Standard Pipe Taper (tapered thread).

Adapter KF-40 to 1.25 in. Male BSPT, Stainless Steel
Flange Size: ISO-KF NW-40
Pipe Thread BSPT (British Standard Pipe Taper): 1.25 in. BSPT-Male
Common Dimensions: A = 2-3/16 inch (55mm), B = 1-5/8 inch (42mm), C = 1-3/8 inch (35mm),
D = 1-3/16 inch (30mm)