This is a new reproduction flexible rubber seal for the evaporator lines to housing on 1973-79 Ford Trucks. All AC trucks have this seal, and the original is almost always brittle and cracked. Note that this version has one 1/2" diameter hole and one 3/4" diameter hole. Some earlier evaporators had two 1/2" tubes, and this won't fit well for those, even though they look similar. 
This is high-quality rubber that will last for years. They are very flexible, yet durable.