This adapter is used to cap off a the threaded outlet from a fitting designed to take 32mm waste pipe. Normally the only way to cap it off is to attach a small length of pipe and then put a cap on the end of the pipe which looks messy and takes up space.

This is designed to be used in conjunction with a 32mm waste fitting such as :- https://www.screwfix.com/p/mcalpine-s23u-multifit-blanking-plug-white-32mm/73053 The nut from any 32mm fitting should work though as long as the nut is removable. I am working on a 3D printed version of the nut itself however getting one from a fitting will always be the strongest option.

UPDATE 2019-07-03 Added the nut from https://www.thingiverse.com/thing:2855169 and a remix with the nut incorporated into the blanking plug. I would still suggest using an original nut as it will be stronger but this version is still handy as a quick fix if needed.