Bolt and Small Part Black Oxide Finish.

[threewood]

I finally got a chance to use a bottle of Caswell Black Oxide dip on a couple of rusty bolts. This is like a parkerized finish. Blasted the bolt, cleaned, dipped for 30 seconds, rinsed and oiled. I'm not certain it is a factory finish but it should work fine.

 

[Macdon221]

I have used this on some fasteners. It works really well to darken the parts. I have sometimes sprayed them with oil based flat clear after dipping to keep them from getting rusty long term. Looks very close to oil. The oil works great too. Just not as long.