I need help with finding the correct names of the connectors which allow a 3/8" tube to slide somewhat securely (but not permanently)into a 1/2" tube. What I mean is that this connector still allow for the 3/8" tube to slide within the 1/2" tube - so it is not screwed in. These connectors are not permanent - but rather "wedge" the 3/8" tube into the 1/2" tube. The connector seems to slip into the end of the 3/8" pipe, which is then secured with a small pinch. The other end of this connector seems to be a 1/2" end, which helps keep the connection tight, instead of loose; but again, allows for the 3/8" tube to slide within the 1/2" tube - thus allowing for adjustability of length. A plastic sleeve then fits over the joint, to give the joint a finished look. I have seen this on a dog barrier for a SUV, where the 1/2" tube is "permanently" affixed to the frame, and the 3/8" tube is then able to slide in and out between the 1/2" tube and the side of the car - so that the dog barrier is then able to adjust easily to different size interiors. I sound like an amatuer, but I am. Can anyone help me find the names of these connectors? How about a source for these connectors? Thank you for any assistance