Inside the nozzle has a turbine that causes the head to spin. The loop is a cutter, the small hole at the tip pierces and the large holes in the back side propel and spray water violently. On the end of a 2 ½" line at about 60psi you can't hold on to it and it will drench you as it leaves your hands. It works great for opening culverts because it cuts and backwashes as it pushes itself deeper into the clog. The intended purpose is to punch a hole in the floor with an axe, insert the nozzle then charge the line. It will take off like the Tazmanian Devil and put the fire out, hence the name "cellar nozzle".
This particular nozzle is in my collection and is stamped FDNY 1921.
