Abstract: A piston head block is provided with smaller exernal diameter at the portion where a cut-out for receiving a lubricant injection nozzle that remaining portion. With the smaller diameter, a clearance or gap is formed between the internal surface of an engine cylinder and the external surface of the smaller diameter portion. Therefore, during piston stroke, the smaller diameter portion, in which the lubricant injection nozzle receptacle cut-out is formed, becomes free from the transverse stress.

Abstract: A method for manufacturing a box-shaped door, which comprises the steps of cutting off the four corners of a rectangular metal blank in the square form to provide the four walls of a box body; vertically bending said cutoff four sides by a female die on whose inner wall there are provided in the stepped state an upper bending section and lower shaping section and a male die whose outer wall is shaped complementary to the inner wall of said female die; curvedly shaping the abutting edges of the corners of the four sides of the metal blank, said vertical bending and curved shaping being carried out at the same time; and welding said abutting edges to provide the box body of a box-shaped door.