Abstract: An electrofusion coupler sleeve for use in connecting together two plastics pipes by fitting the ends into opposite ends of the sleeve and passing an electric current through a resistance heater embedded in the sleeve adjacent its inner surface to fuse together the pipes and the sleeve, incorporates visual indicating means for indicating if the electrical energy supplied has been adequate for proper fusing. The indicating means takes the form of a blind bore extending into the sleeve from the exterior towards the interior. When, in use, the heater is energized, if the electrical energy supplied has been adequate for proper fusing, the softened flowable plastics material is forced, by the pressure produced by heating and fusing, to rise within the blind bore and project from the outer surface of the sleeve.