this is an adjustable table leg leveling foot for round metal table legs with 

inner diameter id=48mm and 

outer diameter od=51mm

feel free to modify the attached openscad file for your needs.

you will need an M10 hex screw and an M10 hex nut as adjusting element.

the screw rests upside down in the bottom part, the nut sits in the upper part.

have fun!