Sometime ago, when I got interested in burying my own loop, I found used butt fusion equipment, though at the time I was not prepared to buy. The videos I had seen of the butt fusion process had cold rings on either side of the pipe. Now that equipment is no longer available to me, I see that socket fusion equipment is less expensive. The socket fusion kits include cold rings, but of the few videos I have seen, none use the cold rings. In any case, with sockets (couplers / tees / et cetera), at best you could only use a cold ring on the pipe side, 'cause is not the socket side a much larger diameter? And the exterior dimension of the socket side not controlled like the pipe side?