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Should holes be threaded?

(-----) 2006

Hi, I am having a part anodized in accordance with AMS A8625 [withdrawn / link is to spec at TechStreet] class III type1. When the parts came back to me, I noticed that the 4-40 threaded holes had been masked. Is that called out in the 8625 spec? It isn't on the print anywhere. I need to turn these parts in today, and I need to know if masking the holes is called out in the ams-a-8625 spec.?

Oscar Draguicevich
machine shop - Pflugerville, Texas

First of three simultaneous responses -- 2006

Thank your anodizer. 4-40 threads are so fine that the etch can destroy them enough that they will not hold. Read a few of the problems that others have written in when threads were anodized.
In answer to your question, the mil-spec does not say that you must anodize threads or that you must mask them.

James Watts
- Navarre, Florida

Second of three simultaneous responses -- 2006

I don't recall if its called out or not, but thank your plater for doing so. Threads that small/fine would have never accepted the screw/bolt had they not been masked (unless you used an oversized tap). And if you had tried to re-tap, there would be a good chance your tap would break.

Marc Green
Marc Green
anodizer - Boise, Idaho

Third of three simultaneous responses -- 2006

First, the AMSA8625 was rescinded and the Mil-A-8625 [link is to free spec spec at Defense Logistics Agency, dla.mil] spec remains the active one.

With regard to the masking, some anodizers believe that threads should never be anodized while some (including me) disagree. Your anodizer may be part of the first camp and it may be their standard procedure to mask off threads. Be that as it may, masking of a customer's part without clarifying with that customer that they want it done seems, to me, fairly presumptuous...

It is definitely not a REQUIRED part of the specification, when used masking is typically done at a charge and with the customer's permission and is PERMISSIBLE (actually, it isn't ever addressed - but, it isn't disallowed, and some parts require it, so by interpretation it is permissible. Sort of like polishing before you start) per the spec. So, a masked part is done in accordance with the spec, but not necessarily in accordance with your purchase order - I would talk directly to your anodizer and find out a) why they did it, b) did they charge you for a process you didn't request and c) if you DO want those threads anodized how they are going to solve your problem.

Be aware, if you re-anodize the part at this point, you will have some material loss on the already anodized portion - your tolerances may well allow it, but you should check to make sure.

Also, they may have masked the area because (depending on depth and configuration) they may think that you are going to get a variable or incomplete finish inside the hole anyway. If they tell you that, they may or may not be correct, but it can be a valid concern.

Good luck!

Jim Gorsich
Accurate Anodizing Inc.
supporting advertiser
Compton, California, USA
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I whole heartedly agree with Jim's statement above. I would never presume to mask a customer's part without their authority, and if required charged accordingly.

There are occasions where threads are used to fixture the parts, but again, the customer would be contacted.

Bill Grayson
metal finishing - San Jose, California, USA


I disagree with a little bit with the above posts. If I saw a 4-40 thread on a part that was requiring a 2 mil hardcoat, I would mask it as a courtesy. Unless, of course, we were talking a a lot of holes, or high volume of parts, which would add significant time to the job. At that point, if higher cost was involved, I would call the customer, and let him know.

At the very least, I would make a call to the customer, and recommend masking the hole.

Thats just good customer service, in my book. In my years of experience, I run into very few customers that actually understand the anodizing process. I try to educate them...in the long run, it makes both our jobs easier.

Marc Green
Marc Green
anodizer - Boise, Idaho


There is a lot of merit to what Marc says, often times the customer is the least knowledgeable about what they want or need and it is our responsibility to educate them. For example, if someone sends me a couple of hundred pounds of aluminum washers and I don't let them know that flat washers are typically problematic with a bulk anodize, my customer service is definitely failing them.

But I would never perform even an "additional" service without checking with the customer first to make sure that they want it - too many times I've had customers surprise me with what their true demands are. With something like this, because the additional service has the potential to make the part unusable (if, for example, they need the threads anodized despite the risk factors), the anodizer really should have contacted them first and gotten their approval.

After all, OFTEN when the customer asks for something wacky it is out of ignorance, but not ALWAYS.

I should note though - I'm not a hardcoater; it may be that this is such an industry standard practice that asking before hand whether or not you want the holes plugged is the equivalent of Jiffy Lube asking if you want them to dispose of your old oil. My specialty is Type II, not type III.

Jim Gorsich
Accurate Anodizing Inc.
supporting advertiser
Compton, California, USA
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