I had a sizer made up for my Star in 0.334″ so I guess one in .331″ with the upper step being .335″ would be what I was looking for.
I recently ordered an expanding mandrel from lee for the .338″ dies and planned on taking that down to the proper diameter to expand my necks. I would much rather do it with one of your expander plugs but trying to make them for varying people’s needs may be a PITA. I could see some wanting the plug for the regular 0.329″ Lee sizer diameter (0.326/.330″) and then a plug for guys like me with a larger diameter sizing dies.