I casted some small hardware using OOMOO® 30 silicon rubber for the mold and Smooth-Cast® 300 urethane plastic for casting. I didn't document the entire process but it's somewhat similar to the method used with my previous mold. The big difference is that this mold is reusable, and I was able to cast several times until I got the quality I wanted.
The bolt and screw were casted from exactly those objects. The coil/spring objects on the right were actually the result of failed casting of the screw. The urethane plastic leaked out of the bottom of my mold but managed to coat the details of the screw's threads. On my last attempt, I was able to cast the fully formed screw after ensuring that no plastic could leak out of the mold.