This is a short stub KF-10 to 1/4 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 10 flange which is more commonly used in the universal world wide vacuum market.

BSPT = British Standard Pipe Taper (tapered thread).

Adapter KF-10 to 1/4 in. Male BSPT, Stainless Steel
Flange Size: ISO-KF NW-10
Pipe Thread BSPT (British Standard Pipe Taper): 1/4 in. BSPT-Male

Common Dimensions:
A = 1-3/16 inch (30mm)
B = 1/2 inch (13mm)
C = 3/8 inch (9mm)
D = 1-3/16 inch (30mm)