Version 1.1 is a fairly accurate replica of the 20x20mm aluminum extrusions which the Creality Ender 3 uses. One could perform a boolean operation between this and another model to end up with a result which will fit into (or onto) the rail accurately. Small adjustments to the result may be necessary since this is a 1:1 scale model.
M20x40 and 40x40 v-rail models are also available.
It was designed completely in Blender v2.80 beta. As a beta version, support for the .blend file may break at any time; I'll try to update it with the stable version once that is released.