Stainless steel hex bolts made in Japan. [How to calculate the thread length of the mm screw bolt]: Up to 5.0 inches (129 mm): bolt diameter x 2+6, under neck 5.1 - 8.6 inches (130 - 219 mm): bolt diameter x 0.07 inches (2 + 12 mm), lower neck x 8.7 inches (2 + 25 mm).