A. You will need to measure the outside diameter of your copper tubing. Whatever the outside diameter of your copper tubing is will be the size of the compression fitting you will need. For instance, if the outside diameter of your copper tubing is 1/4" then the compression fitting will need to be 1/4".
Compression fittings are not sized like copper sweat fittings.
Q. "I have clear vinyl tubing, can I use these compression fittings with it?" A. These compression fittings will work on some sizes of clear vinyl tubing and most sizes of low density polyethylene tubing. However, it really depends on the outside and the inside diameter of the plastic tubing to be used. When using plastic tubing, the "plastic sleeve" must be used and the "brass insert" must be used. The plastic sleeve is used to seal against the outside of the plastic tubing and the tapered end will seal into the compression fitting. Plastic sleeves are used because the brass compression sleeves can more easily cut into the plastic tubing, potentially causing a leak. The brass insert is used to keep the inside of the plastic tubing from collapsing as the compression fitting is tightened. The size of the plastic sleeve and the brass insert must be chosen according to the outside diameter dimension of the plastic tubing to be used. The brass insert must be able to fit snugly inside the plastic tubing while still allowing the plastic sleeve and compression nut to slide over the outside of the plastic tubing.
