Airbrush Air Hose Connector 1/4 BSP Male – 1/4 BSP Male x 2

Airbrush Air Hose Connector – BSP stands for British Standard Pipe thread.
This is the pitch, width and depth of the thread on the pipe.

You not only need to get the right diameter but also the correct thread type to couple to it.
A 1/4 BSP fitting is commonly described as a 1/4″ fitting which is not exactly correct as the diameter is approximately 11.75mm (approx. 0.46 of an inch).

This connector can be used to join a 1/4 BSP Female air hose outlet to a 1/4 Female air hose outlet