EvilEyez...I bought my spacers at a 4x4 shop! They have them manufactured to their specs to sell retail. They use 6061 billett alum just like the brand names, and steel (of course) studs. The spacers are very substantial pieces of metal, but light, so not much inertia when spinning. The vehicle doesn't even know they are there, in between wheel and rotor hub.
This shop installs these on all kinds of off road vehicles including rock crawlers! They told me that no one has ever reported a failure! Mine were intended for use on a Jeep or F150 (5x4.5).
Just my $.02 for your consideration.