Spring loaded wheel and slide types are available to maintain the source stop in the center of the pipe and yet pass freely over the welds. Used with rigid source tubes the devices can be pushed easily along distances up to the limit of the source projector. They are available with threaded fittings on both ends (compatible with the guide tubes), or the standard male thread at one end and an integral source stop on the other. The standard length is 7 feet. Other lengths are available upon request.
