Is Black Oxide Finish Hard to Apply to a Screw?

What I need: 10-32 knurled head thumb screw black 2.5" long; head less than 3/4" diameter.  All that I can find are too short..

I know some of you have lathes with threading and knurling attachments and could turn four of those out for me with almost no effort.   But they are going into an optical assembly so they need to be black.  How hard is applying a black oxide finish (thin of course so it threads easily into receiving part)?  Is gun bluing similar to black oxide in darkness?

Thank you for all the black oxide responses.   I just realized that I do not need the threading attachment.   I can start with a 3/4" steel rod turn it to the correct size and use my 10-32 die to thread it (I really only need about 1" threaded) and then black oxide it.

I briefly considered making the part of aluminum but I cannot find a blackening process that I can do at home on aluminum. 

I still do not have a knurling method but almost as good: put the thumbscrew in the chuck on a rotary table at a 90 degree angle.  Use a fine center drill to slice a line down the head perhaps .01" deep, turn it five degrees and repeat.  If I had a CNC rotary table, I would do it every degree but I think 72 lines would make it adequately grippable.  This is also roughly the sane as straight line knurling without the knurling device.  I would also cut a series of concentric circles using a center drill while rotating the thumbscrew 360 degrees.  Not as pretty as diamond pattern knurling but probably adequate for turning with my finger.