fusion 360 part link: https://a360.co/2K7Y30J
This design can be adjusted to your needs (or to the things you already have) by changing the parameters in fusion 360. Don't make too big adjustments at a time as that may sometimes result in some weirdness with the model.
The size of the rods can be found using the measure tool in fusion 360.
To join the two parts in the middle an M6 bolt and nut are used.
No support needed and just use the materials you have or want.
Hope you like it and have fun with it.
[the included stl's are an example for a 150mm deep shelf bracket. The rod diameter is 8mm. The following rod lengths are needed; 113,7mm (4x); 81.6mm (2x); 35.3mm (2x).]