Fiberglass shafts were the 'carbon' of years past. They came spined for low and high weight bows just like aluminum shafts. They were supplied with both glue-on and later, screw-in inserts. The best shafts (in my opinion) were MicroFlites first sold by Frank Eicholtz an innovative San Diego bowyer who first used fiberglass to face his bows. Fred Anderson learned his trade working for Eicholtz.
Other providers of glass shafts were Gordon, Gilmore, Black Hawk, Graphlex, Dura, Mercury, Herters, Glashaft and Bingham. I know that Gordon and MicroFlite manufactured their own. Bear Archery used MicroFlites for their Kodiak Supreme arrows. Each manufacturer had their own spine charts. I use #8 Microflites (cut 29")for my 50# recurves and longbows. The wall thicknesses on glass are thicker than on aluminum, for the same spine, but you can get away with using aluminum arrow inserts on some glass shafts. Ray