The 13/21 reinforced silicone tubing is flexible enough to fit on our Craft Hardware 19mm OD Hose barb fittings. It is tight once installed but you should always use a hose clamp to make sure it will not come off. You do not need to heat the tubing to install it on the hose barb. Simply insert the tubing at an angle to the hose barb to catch one side of the tube. Then push the tubing over the hose barb completely. You can make small adjustments so that the tubing is on straight. Tighten your hose clamp. Done!