Square tube corner 12.8 (.5") HK

I remixed the part to fit the aluminium square tubes which HobbyKing sells, link to item in Europe store:
http://www.hobbyking.com/hobbyking/store/__61707__Aluminum_Square_Tube_DIY_Multi_Rotor_12_8x12_8x400mm_5Inch_black_EU_Warehouse_.html

Settings used with .scad file madmike8 shared (inlcuded with the settings I used):

Tube_Outside_Size = 13.1;
Wall_Thickness = 0.95;

Printed in PLA, ended up with a tight and solid fit.