Bumax, which is in the same strength class 10.9 as that of steel bolts although it is stainless steel, has strength (yield stress) four and two times that of SUS304 (A2-50) and SUS316 (A4-70), respectively, which are used for general stainless steel bolts. In Bumax, the 20-millimeter diameter bolt design of SUS304 (A2-50) can be downsized to 10-millimeter diameter, achieving a weight reduction to 1/4.