3/8" round fiberglass rods are suitable for 32" overall-length weapons MAXIMUM. I've had to cut an old one of mine all the way down to 30" to keep it from failing flex over time.
TSC might be selling you 1/2" round fiber rods, though, which, for people who hit lightly, can be suitable for 48.01" reds for ~6 months to a year before it flexes out and are otherwise fine for most blues.
Vali: I'm not a fan of dual coring. You end up with a core with very strange flex characteristics which can make it unpredictable when swung and lead to weird flatting incidents. Also, it's heavier and bulkier than the equivalent single core. Also also: How'd you get a core 1.5" wide by putting two 3/8" rods together?
I recommend, for all of your bluesword needs: .524 kitespar from Goodwinds Kites
. Super-heavy hitters I know have yet to snap it, I've yet to snap it, it's a good diameter to build off of (not too small, not too large), and it's light, so you can make light swords or heavy, very well-counterweighted swords. I've built 12.8 oz swords and 19 oz swords at ~34" with it. I buy the 64" lengths and halve them, basically.
Otherwise, if you're dead-set on a solid core, go for 1/2" round fiber or 3/8" square fiberglass (for swords under 42") or 1/2" square fiberglass (for min-reds and heavy heavy blues). Of course, I don't know where to get square fiberglass right now... But you can order round fiberglass from: http://electric-horse-fence.com/electric_fence_posts/fiberglass_posts_braces_acccessories/fiberglass_posts.htm#halfinch