I think that you have experienced a "one of" in quality control with the centering ring. I have built pretty well all of the RTB line, in some instances multiples. I have never had issues with the CR fit that could not be resolved by running a thumb nail along the inside edge of the "inner" tube. I never try to press the ring any more than flush with the tube end. The instructions are pretty explicit in the fitment of the two differing sized and coloured rings to ensure that the motor tube correctly fits in the main tube and inner tube. I have heard of some reversing the fit on the motor tube and then being completely threaded, but not an issue with fit.

Not saying that you did anything wrong, just that I have not seen this as being a common problem with the fit of the CR-79 into the ST-950SC. Given the intent of the line and the focus on relative newcomers to the hobby (especially with the aptly named "Start"), I am confident that this should be the case.

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