Over time, as the wood in a structure shrinks, continuous-rod seismic hold-downs can loosen and become less effective. The RAS Nut by Ratcheting Anchor Systems moves with the structure to stay tight, says the maker. One-way ratcheting threads allow the nut to slide down a threaded rod while locking tight against uplift forces. Wood screws attach the nut to the wall plate so that it moves down with the wall. The nut is sold in six sizes, from 1/2 inch to 1 1/4 inches, for $16 and up. Ratcheting Anchor Systems, 408/866-2525, ras-nut.com.