Super strong, and a super complete package. Every single part needed, even tubing and mounting screws. Even an air guage! Even steering cables! Even a needle valve to slow the retracts down for scale appearance! These are ALL METAL, not a scrap of plastic on them. Very easy to install and set up, very forgiving. These are air-up and air-down. Suitable for 40-140 sized planes. We also have struts for them.