Thermpolastic pipe coupling

Claim 1

A coupling for joining lengths of plastic pipe comprising in combination: a. a hollow cylindrical member adapted at one end for fixed attachment to a first length of pipe and having: 1. an externally threaded portion, 2. a tapered internal socket located at the end oposite the end for fixed attachment to said first length of pipe, said internal socket tapering axially inward toward a shoulder stop adapted to abut the end of a second length of plastic pipe inserted inside said socket, an internally threaded collet disposed outwardly of said socket having a continuously varying thread depth tapering axially outward from the outermost extremity of said collet toward said socket and longitudinal slots extending inwardly from the outermost extremity of said threaded collet thereby permitting movement of said collet radially inward and axially toward said shoulder stop to engage the second length of plastic pipe with said internal threads and to compress the end of said second pipe against said shoulder stop; b. a cylindrical locking nut adapted to fit over the end of said second length of plastic pipe, having internal threads at one end for operable engagement with the external threads of said cylindrical member and a tapered inner surface at the other end for urging said threaded collet of the cylindrical member radially inward and axially toward said shoulder stop into locking engagement with the end of said second length of plastic pipe when said second length of pipe is abutting said internal shoulder stop of the cylindrical membEr.