L Joining plates.
Makershop's "L" joining plate is a 2mm thick solid aluminium. plate. They are stronger than the plastic version They have been anodised black.
The L bracket can be used in 3 ways - it can be used to join two pieces together in an "L configuration, or as a 45 degree brace, or it can be used to join 3 pieces together with 2x 45 degree cross brace.