From ATS: https://www.aircraft-tool.com/Detail?id=142
High-Quality Bucking Bar from Aircraft Tool Supply
Weight & Dimensions: Weighs 2 lbs, measures 6-1/4 x 1 x 2.5 inches
Construction: Heat-treated, polished working surfaces for durability
Usage: Ideal for bucking rivets, with a polished finish for smooth operation
Additional Info: Technical data available via provided link: https://www.aircraft-tool.com/techdocs/bbar/142.pdf