Hi All, when I was a youngster (many years ago) my older brother and I used to play with a 'rocket motor' for models which I think was called a "JETX". These little units were basically a hollow tube that containrd a couple of pellets (of unknown material) and a "thrust cap" which was basically a screw-on cap with a small hole to allow the combustion products to exit in a high velocity fashon. They would propel our little balsa wood model airplanes very nicely, to a velocity that could assure a flight of much longer duration than we could acheive with a hand launch. They offerred, as an option, a 'thrust improver' that looked very much like the devices shown in the website refferred to as "xxxx" (I can not remember the name right now. Sorry for the CRS Syndrome symptom). These devices worked. Thrust was improved by at least 20%, by actual testing of verticle endurance timing with a stopwatch (high tech in the '50s). Therefore, the concept of the thrust enhancing effects of these XXXX nozzles is supported. OK. WHAT WAS THE NAME AGAIN????? Eric Thompson S/V Procrastinator South San Francisco capteric36@sbcglobal.net