Acceleration Control Ring.

The basic idea and execution of an exhaust restriction throttle of one sort or another on the single collected lateral exhaust of glow model engines preceded any Cox effort by several years. The ringed exhaust restrictor was simply a refinement/adaptation to work with Cox's cylinder design. (and Cox's set up did indeed work considerably better) In the sub-miniature class engine category, the Anderson/Jim Walker Spitfire .065 and Wen Mac MK II .049s came out with lateral exhaust collector throttle restrictors before Cox did its "ring thing". AMF Wen Mac also came out with a "ring thing" throttle restrictor for use on its glow head Hot Shot series engine powered Lotus race car and Boeing Pea Shooter plane. (circa 1965) This throttle is also very effective, though I don't like the mechanics of its linkage system which needs hacking for practical use on a built R/C plane. I'll leave it to others to say who was first with the "ring thing".

My quickie research of archives and Hepperle suggests that Cox's first use of a "Ring Thing" throttle was circa 1969 on the Medallion R/C and then the early seventies on 190 and 290 series product engines. So AMF Wen Mac may have beat them to it circa 1965 Hotshot powered Boeing Pea Shooter and Lotus race car.

Having played with various COX RC and Tarnot RC carbs as well as with exhaust throttle rings, my experience shows the exhaust throttle ring provides the better rpm control, and if throttle ring is used and the stock carb remains on the engine the top rpm achievable with the stock TD carb is higher than with RC carb  thanks to  the more perfect atomization of fuel in a stock  COX carb than in a COX RC or Tarnot carb...let alone the poorer fuel suction with the unscreened RC carbs. On top of this, no special glow head with hot plug to reach low and stable idle is required with the use of exhaust throttle ring.

So I tend to swap my RC carbs with stock carbs and use exhaust throttles instead, that are visually less appealing/elegant but work better for me. Maybe out of some nostalgia I will reswap them sometime soon but now I am having my exhaust throttle ring period..

The only downside of exhaust throttle rings is some have caused excessive abrasion on the lowermost cylinder cooling fin that finally detached. Maybe the vibration..To prevent this I bend a thin ring from a servo  pushrod/ piano wire and pull it on the cylinder up to the lowermost fin to protect the fin from the continuous abrasion by the ring vibration..with a thin enough  wire the throttle ring height is still OK..if not, the bottom of the ring is sanded a bit so that the ring should not get stuck when the cylinder is tightened in the crankcase.

Sorry that my post missed the historical details.