There is no problem with the product, but due to the super low head the tightening is off with a normal wrench, how much you lick the hex head with stainless steel. It is safe to use an eyewear wrench when using an ultra-low head. And the unit price is too high. From now on, use carbide rotary bar to cut it or switch to hexagon socket head bolt (stainless steel). Prior to purchasing ultra-low head hexagon bolt (stainless steel), I was processing one size smaller head size of hexagon bolt. Example: M6 is 10 mm, but M5 was 8 mm, so it was scraped 1 mm per side. In the part where the wrench size becomes smaller, screw tightening was done securely even in a narrow place.