Compression fittings are commonly used with hardline setups, and air suspension kits from brands like D2 Racing and KSport. Compression fittings make a great seal on both standard nylon air line and hardlines but they are less convenient than PTC fittings since there is no way to easily disconnect the air lines on the fly without tools. If you have any questions about compression fittings and which ones will work best for your setup, contact a Bag Riders air ride specialist for a recommendation!