Tools of the Trade.

Bookbinder Tools — Bone Folders.
Printer Tools — Pica Gauge.
In use everyday around here, these cow-bone tools enforce a razor-sharp edge on folded paper, dustjacket protectors, and myriad other tasks. Conversely, they can help keep a stubborn folded sheet stay open when applied to the fold; pressure permits a minor breaking of paper fibers and, therefore, re-alignment.

For scale, a type gauge shows inches (and picas). It has a right-angle hook on the domed end that grabs the end of a type stick into which handset type is placed.