The parts you will find here are ones that I developed to help me put together rockets. The most useful, in my mind, are the nut holders and fin holders (although the Wiring Assistant is a close second with the time it saves me). The nut holders allow you to "fix" machine screw nuts to the inside of a coupler or airframe body tube. This allows you to remove guides for painting and also allow for quick field replacement of damaged parts. The fin holder can be used to keep a fin in place while glue is setting.
These nut holders have two 6-32 nuts spaced at the required distance for mounting the great (personal opinion) 1010 rail guides that Public Missiles Ltd makes. This product also contains the required flat head screws needed to mount the guides.