Building Long Thumbscrews

I mentioned a while back my need for thumbscrews (preferably lobe handles) for a new ScopeRoller product.  I received useful help, and have now discovered that long enough thumbscrews are not readily available.  But the parts exist to build my own.  The pad that presses down on the ground is a 1/2"-13 threaded part with a 15 degree swivel.  This is the lobed head that the 1/2"-13 bolt screws through.  Fully threaded 6" long 1/2"-13 bolts are readily available.  Solution.  The only part of the project that is uncertain is whether the 1/8" aluminum plates that I was planning to use will tolerate repeated strain of steel bolts on the threads.  If not, 1/16" steel plates.