These fittings are excellent for air horns or vehicle air ride suspensions.
In order to get a good air tight seal that doesn't leak, be sure you cut off the tubing square. Most leaks are caused by tubing being cut at an angle and not fully covering the barbs.
If you are having difficulty getting the tubing onto the fitting you can try 3 possible options: put some soapy water on the barb, warm the tubing up (DON'T USE A HEAT GUN) or you can just spit on it. There is no need for hose clamps as the barbs are designed to be a perfectly snug fit.