The surface treatment of the bolt is probably black stain, that is, it is considered to be only black stain on the SCM material fabric. I rust. There are UNIQLO, chromate, other surface treatments if you consider rust prevention. But the other one is rusty. I think that the surface treated bolt suitable for the purpose of use is good. Even if it is screwed in by other person, it is unpleasant as it can not be screwed to the base of the head of the cap bolt. Normally there is no usual use of a washer or a combination of lock washer and taper washer dedicated to cap bolt. Since there are quite a variety of suitable positions and methods of use, we recommend that you are recommending "Screw list" so it is surprisingly cheap, so you better purchase it and increase your knowledge, you should also upgrade yourself. It is difficult to close the vault relationship. It is recommended to carefully examine materials and hardness etc. (although surface treatment is also true). I would be pleased if you could refer.
Automotive bolts (detailed items) are saved because there are few stocks at home centers. Recently the number of automobile parts store in town has decreased, and the place where we have inventory of bolts has become less