Those cast adaptors are junk. There isn't enough material around the second set of studs. They'll work for awhile, but they're prone to cracks even with normal use.
They make billet adaptors that are similar that will work just fine if properly torqued. The problem is that most of them are 1" thick. Those cheap cast adaptors are usually 3/4", so if your wheels fit now they may not with a thicker adaptor.
