To provide connection parts for castings having reduced weight and high strength while dispensing with welding work.

A boom top 1 of a casting includes two supporting plates (a first bracket 11 and a second bracket) and an intermediate supporting member 2 arranged between two supporting plates. The intermediate supporting member 2 has (i) a bottom plate 21 having a hole 21h for taking out mold and (ii) a cover plate 22 covering the hole 21h for taking out mold. A protruding part 21t protruding along the direction D for taking out mold is formed at the whole periphery of an edge part 21r facing the hole for taking out mold of the bottom plate 21.