For your edification, an example of a Buckner 1310R full-circle rotor head. No gears. Water goes through the angled slots, and moves a free-floating brass cylinder in a circle, which contacts a brass plate, to which the nozzles are connected. Where the plates contact each other, is a sort of hill and valley pattern, which gives the head its 'cam drive' name. Same sort of 'controlled friction' bearing washers that impact heads used. The inlet is 3/4 inch, and the optional screen keeps sand from causing trouble. The speed is adjustable by moving a threaded plug to cover/uncover a bypass port. Dual opposing nozzles provide distance and close-in coverage, with the slotted nozzle fanning some water straight up, to fall near the head. This deluxe, rubber-covered model pops the nozzles up only a fraction of an inch above the rim. It stands all of four-and-half inches tall. The standard 1300 series heads didn't have the upper canister, and sprayed from a central spindle that popped up less than an inch. The standard heads stood about three inches tall. This particular specimen could spray almost forty feet at thirty psi, if equipped with the larger (3/16") of the two distance nozzles. Stainless steel machine screws could be removed, and the guts of the head puled out from above.