John Guest Speedfit 5/8" BSP to 3/8" shank fitting PI451215FS

These fittings will screw onto standard tap shanks and allow 3/8 OD beerline to be attached. 3/8 to 3/16 reducers can also be used with this fitting to give a quick an easy reduction to 3/16 from the shank (see photo) 

OD - outside dimension

Used by the drinks industry and homebrewers all over the world. Pushing the tube into the fitting is all that is needed to produce an instant but permanent leakproof connection. The fittings are just as easy to disconnect and re-use without the need for replacement parts.

Once you use these you won't go back to barbs and hose clamps.