This is a fence for No 71 Stanley Hand Router/Plane.
Seems to print in PLA at 30% honeycomb infill quite well, although you may want to add support for the screw slow.
The screw needed to attach this to the Hand Router is a 3/16" Whitworth (24 tpi) (also known as a 10-24) which can be found on ebay if your in the UK.
Designed in Sketchup and then exported as an STL. When testing I made smaller slicers of the part so that the print faster and I can fail fast.