Bracket is the part that used to attach whole system to the arm
Uniball bearing housing is aluminum.
Yes, i would too prefer aluminum, definetly the 7075 T6 series aluminum, but steel bracket is in this pricerange.
Strengths: Normal steel is 355N / mm2, 6082 T6 aluminum is 270N / mm2, 7075 T6 aluminum is about 500N / mm2