This is a short stub KF-25 to 3/4 inch MALE G BSPP. This thread size is primarily used in Europe and Great Britain. This adapter converts "G" BSPP thread to a KF 25 flange which is more commonly used in the universal world wide vacuum market.
BSPP = British Standard Pipe Parallel (straight thread) and is often noted G, for example, G(3/4).
Adapter KF-25 to 3/4 in. Male BSPP, Stainless Steel
Flange Size: ISO-KF NW-25
Pipe Thread BSPP (British Standard Pipe Parallel): 3/4 in. BSPP-Male
Common Dimensions: A = 1-9/16 inch (40mm), B = 1-1/16 inch (26mm), C = 13/16 inch (20mm), D = 1-3/16 inch (30mm)