Screw threads: to anno or not to anno?

[neftaly]

I've got some 6061 bodies to hard anodize with a few blind M4/M5 tapped holes, a blind 9/16-24 and an open 1/8 NPT. In regards to stripping/crossthreading/wear resistance, is it better to plug them up or leave them open when anodizing?

The M4/M5 are about 4mm deep and the 9/16-24 no less than 8mm. The holes will take mostly SS 303 hardware, but the 1/8 NPT may receive a plated brass fitting (or possibly Annoed 6061).

[theboss33]

They will be more durable if they are annoed. It is when you are stripping factory anno you want to stay away from the threads. I have a pile of scrap because the guys doing my anno work had to redo parts a couple of times and now there are no threads left in the parts.

[evil_racecocker]

To add on what boss said,

Usually one re-anno won't damage threads (asuming the anodizer knows what he is doing). It is when you get into the 3-4 annos is when threads dissapear. I have a 98 STO that has been anodized 5 times over it's life. All the threads on the bottom of the body had to be helicoiled, and I had to make a new bolt as the upper tube was now .008 oversize. But she is damn sexy and functions flawlessly.

[neftaly]

They're raw/freshly machined, and I have some helicoils for the M4/M5 just in case (but will def plug them if they have to be re-annoed). So the change in diameter/thread pitch isn't really worth worrying about?

[evil_racecocker]

You will be fine. Type 2 anodizing only ads about 25 microns to the surface thickness (about 0.000984).

[neftaly]

Great, thanks.