A Compression fitting is made up of a body, a nut and a deformable ring, commonly referred to as an olive. When the nut is tightened, the olive is compressed between the nut and the receiving fitting; the ends of the olive clamp around the tube, sealing the space between the tube nut, and fitting body, thereby forming a tight joint. Some compression fittings may employ elastomer seal to help form the joint.
Compression fittings allow easy, heat-free joining of tubes which means no hot works permits are required and joints can be made where it would otherwise be dangerous to use a naked flame. These fittings can be taken apart again, but the olives / deformable rings etc. need to be replaced if the fitting is to be reused. Joints can be made on wet pipework, making them ideal for use in maintenance and repair applications where the complete draining of pipework is difficult.
Typically, these fittings are manufactured from a range of materials that compliments the tubes that they are being used with.