Genuine Merrill R-121R complete fine threaded head for Merrill R6000 Yard Hydrant. The R-121R looks identical to the model R-121, however the threads that connect the head to the pipe on the R-121R are fine thread. This head comes complete, and is made of cast iron. When replacing the head it is a good idea to replace the plunger since the head is already off. Merrill R121R.