A threading or rethreading die made up of a plurality of complementary separable interfitting parts held together by a tension spring disposed around the exterior surface thereof which in use are separated from one another under the tension of the spring thereby enabling the die to be passed over a member to be threaded or rethreaded whereat the separating force is relaxed permitting the parts to re-engage on the member. The die is then turned to effect the cutting of the threads.