Parametric corner bracket (external) with round countersunk holes

Remix from https://www.thingiverse.com/thing:2862925 to make external corners instead of internal. Hole facets for screw heads moved to external side.
Use "Open in customizer" to make corner as you wish

Whole fame goes to author of original. My changes are small.

PS. As the customizer is working poorly or even not at all I recommend using free OpenScad with code downloaded from this page.
Full instruction is there: https://www.thingiverse.com/thing:2815234