Growth rings are the very light tan colored lines running the length of the shaft. They can be seen while the shaft is lying flat and if the shaft doesn't yet have an insert and deco rings you will see the lines/rings on the end-view. They will appear on the surface approx. 180 degrees apart, same with the spine. The spine is the 'checkered' figure, approx. 1/8" wide that runs down the center of the shaft (on the surface). On a premium grade shaft the spine & GRs should run straight down the length of the shaft from one end to the other. There should be no run-off. That's where the GRs fade to one side or the other and start to run off the shaft. Shafts that have severe run-off are more prone to warping. The internal stresses that caused the wood to bend, thereby causing the run-off, are still present and still active. Over time, they will prevail. Because a shaft is tapered, the outside rings on the big end will disappear as they travel up the shaft due to the shaft's diameter getting smaller. Those disappearing rings should do so at approx. the same length down the shaft. Now to GR count.
The higher the GR count in a 1" diameter dowel, the denser the wood. This is the result of the tree experiencing many dry years of growth. Not totally dry but less rain than in other groups of years. It's very possible to get high GR count shafts & low GR count shafts from the same tree.
Trees that experience a very damp climate, such as the Big Leaf Maple, native to our Great NW, will have GRs very wide apart from one another because the tree is able to take-up all the water it can stand and grow pretty quickly, comparatively speaking. This wood is soft, unstable and unsuitable for cues (unless cored).
Generally, the most desirable wood for shafts is straight grain hard rock maple, more commonly known as sugar maple. Preferably grown in climates that have an avg. growing season but particularly cold winters. This wood is found in abundance in Upper Michigan and Canada as well as other areas with similar climate. We have several wood specialists that frequent here that may be able to provide additional info.
IF KJ GOING TO WRITE A BOOK.