Wouldn't advise PVC or any thermoplastic material for spreaders. Such materials are not nearly stiff enough to take the combined compression
and cantilever loads presented to spreaders, even at normal temperatures. Then consider what happens if you have the boat
sitting in hot sunlight for a while... yikes!
Didn't see your previous post about the "nubs", but one could consider using 1" diam aluminum tube with a short machined 1" ID adaptor at the join, possibly best welded to the spreader itself. Shouldn't be so very expensive...
Good luck, and cheers,
Jim and Ann s/v Insatiable II lying Lake MacQuarie, NSW, Oz
PS You do realize that if a spreader collapses while sailing the mast
will surely be destroyed...