Join three 40x40 V-slot profiles together with this new brackets designed specifically for the 40x40 profiles.
40x40 Cube Corner
Please feel free to make, hack and use as you please.
Finished products can be found here: https://makersupplies.dk
More info in this video:

40x40 Cube Corner 2019-08-23
An oversize version of the Cube Corner that fit 40x40 V-slot profile