John Guest Speedfit 3/8 to 3/16 stem reducer
Regular price £2.50
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.