Inspired by ducktaperules' design, this is a way to isolate Z wobble from the printhead. The only difference is that this is designed for the 3/8" ACME screws supplied in the upgrade kit.
Print 'em out, one for each side. Slip the nuts into the slots. They should not be flush, as some of the wood on the plus gets in the way. Instead, let the nuts sit flush on the wood, with these slightly lower down.