Many diaphragm and small vacuum pumps come with G BSPP intake and exhaust thread ports. These 1 Inch G to KF-25 fitting adapters convert "G" BSPP thread to a KF-25 flange which is more commonly used in the universal world wide vacuum market. This thread size is primarily used in Europe and Great Britain.

BSPP = British Standard Pipe Parallel (straight thread) and is often noted G, for example, G(1).

Adapter KF-25 Flange to 1 inch Male BSPP Thread (British Standard Pipe Parallel), Stainless Steel
Common Dimensions:
A = 1-9/16 inch (40mm)
B = 1-3/8 inch (35mm)
C = 1 inch (25.40mm)
D = 1-6/8 inch (45mm)

These KF25 adapters screw into pump inlet and or exhaust for easy connection to standard ISO KF or NW roughing line fittings.