The aluminum bracket is made from Aircraft grade aluminum - T 6063 T6 / extruded by a machine and therefore has a tolerance less than +/- 0,05mm
The steel bracket is made from 10-gauge sheet metal steel bent by a machine that is fed by hand by person, therefore the tolerances are much higher.
The male and female components of the aluminum bracket can be interchanged with different batches, whereas the steel bracket's male and female components cannot be interchanged with another's length of bracket due to the custom nature of the steel version.