Aloha, fun & authoritative answers -- no cost, no registration, no passwords, no popups
(as an eBay Partner & Amazon Affiliate we earn from qualifying purchases)

Home /
Site 🔍
pub  Where the
world gathers for metal finishing
Q&As since 1989

this text gets replaced with bannerText
spacer gets replaced with bannerImages

Jump to this related thread:

Topic 2906 "Plating external threads: dimensional effects"

Topic 12211 "Thread dimensions after plating"

Topic 51293 "Zinc plating blind holes / threaded holes"

Topic 57493 "Zinc Plating Internal Threads: dimensional changes & coverage issues"

• or continue with -----

Zinc Plating Thickness and Tolerance on Fasteners

Q. What is a reasonable thickness and tolerance to require for electrodeposited zinc on parts with external threads? We have experienced substantial fallout on external threaded parts requiring zinc plating that do not pass after-plate thread ring gages. Our preplate gages have been setup to allow for .0001-.00035" plate thickness. Our current plating supplier is asking for us to loosen the tolerance to .0002"-.0005" stating that this is as good as the industry can provide. I have several concerns with doing this: the cost of new pre-plate gaging, the effect of .0005" plating thickness on the 60 deg. thread form, extensive print changes, and conflict with our existing customer prints.

Gary Buell
- Fond du Lac, Wisconsin

A. Hi Gary. The answer will depend in large part on what average or minimum plating thickness you are specifying. It's unusual to spec less than .0002" average plating thickness, so .0002"-.0005" doesn't sound at all unreasonable to me.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

A. Gary & Ted, this might sound as a very stupid comment, but we have encountered this problems in the past and some clients don't consider that the thickness of the deposit has to be counted double when considering a round diameter. Thickness in each side of the part.
Also, in special applications the thickness on the threads is considered that it affects 4 parts of the thread; the right hand side of the thread (crest), the left side of the same thread and the same happens on the other side of the fastener.

Now, what are you using as a nut? Have you considered the thickness on this part also? All of these increase the original diameter. I hope this helps.

Enrique Segoviare
- Monterrey, Mexico

Q. To shed more light on our zinc plating thickness issue, most of our in-house thread ring gages are class 2A gages. In the past we have attempted to produce threads to an undersize pitch diameter (less 4 times plating thickness) and use the 2A gages to check afterplate condition. If I'm reading SAE J476A correctly we should be allowed to go to class 3A gages to allow for the thread growth on external threads. Is the class 3A gaging option more forgiving for a thicker plating allowance (.0002-.0005")?

Gary Buell [returning]
- Fond du Lac, Wisconsin


Q. What should be minimum coating thickness for zinc plating on mounting pan of electrical load centers?

Syed Hussain
manufacturing engineer - Riyadh, Centeral, Saudi Arabia
April 28, 2009

"Zinc Plating"
by Herb Geduld

on AbeBooks

or Amazon

(affil links)

A. Hi, Syed. I am familiar with plating but not with IEEE or NEMA or other standards that might dictate plating thickness for this particular application. If there are no such standards, and this application is indoors in a relatively benign environment, then 5 µm (0.0002") minimum would be a good place to start because that's pretty much the commercial minimum. Good luck.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. Dear all,
I need to zinc plate (and gold passivate) a screw of dia. 42 mm & length 200 mm.
The customer has mentioned reduction in effective dia. of .152 mm.
How can I specify the plating; what is the standard I have to refer to?

kavi prakash
control valves - nashik, India
January 6, 2010

A. Hi Kavi. ASTM B633 is a very common spec for zinc plating. The minimum thickness is 5 µm.

Luck & Regards,

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Thickness of alkaline zinc plating


manoj kumar
January 5, 2015

A. Hi manoj. The application matters: there is no standard thickness which is irrespective of the application. Rather, a thickness is specified based on the service conditions. ASTM B633 is one of the better known standards which defines required thickness vs. service conditions:
5 µm for mild service
8 µm for moderate service
13 µm for severe service
25 µm for very severe service

Good luck.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. Hi, Good day, I am Manikandaprabu, We are using Boron steel with zinc plating and olive drab passivation for SELF TAPPING SCREW ST 4.2x13-C that is used in drain hose assembly of washing machine.Currently our plating thickness is Fe/Zn 12.5 microns and for cost effectiveness shall I reduce it to Fe/Zn 8

Manikandaprabu janarthanam
- Neyveli, Tamilnadu, India
April 30, 2019

A. Hi Manikandaprabu. That doesn't strike me as unreasonable as long as there are no industry standards which you have agreed to meet which call for the thicker plating.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
April 2019

Q. What is a safe plating that should not cause binding in the threads for a #6 screw?

If the allowance of an #6-32 UNC-2B screw is .0008" and I use Fe/Zn 5ANS per ASTM F1941/F1941M-16 I should be fine because 5 microns is t=.0002" and multiplied by 4 then the pitch diameter of the screw is increased by .0008".

If the finish is at a minimum .0002" is there a binding risk because the plating doesn't specify a max tolerance?

Is my math correct or can I get by with Fe/Zn 8ANS per F1941?

Cameron Schmid
Transit - Chicago, Illinois, USA
May 14, 2019

A. The thread gauge should be your guide, make sure the incoming material has tolerance for plating thickness and the outgoing part also meets the post plating thread gauge.

4Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind
supporting advertiser
Bengaluru, India
Saify logo

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Chemicals &
Consult'g, Train'g
& Software

About/Contact  -  Privacy Policy  -  ©1995-2024, Pine Beach, New Jersey, USA  -  about "affil links"