Abstract: A pipe coupling comprising a first and second pipe and a nut cooperating with the thread joint of one of the end pieces of one of the pipes by drawing against the latter a second endpiece belonging to the other pipe. A movable locking member, biased by a spring, comprises a shaped portion which in a locking position, fits onto a complementary shaped portion of the nut, thereby preventing the latter from turning in relation to the endpiece onto which it is screwed. The locking element is slidingly mounted on a support member which is fitted onto the first pipe so as to extend about the thread joint, wherein a sufficient radial distance is maintained with the latter to allow for the passage of the nut. The coupling is suitable for fitting, and even retrofitting,to standard couplings, especially of the nipple-nut type.