Thread Before and After Plating (Part 2)

How to Control the Thread Size Before Plating?

As it is mentioned previously, the goal of OD control can be easily reached under stable CNC processing. Generally, after CNC processing, the threads of a non-plated component have to pass the thread gauge inspection so as to pass the QC inspection. Nevertheless, for components that need to undergo plating process, the manufacturing and inspection procedures will be different from the former. According to the requirement of our Swiss dental equipment supplier client, APPORO has to be discreet than ever for inspections. See the examples below:

Based on the required plating film thickness, APPORO has to leave some room for it during CNC processing, and use the pre-plated thread gauges for inspections. See the photo below. If the required plating film thickness is 1-3um, the major, pitch, and minor diameters should all be +0.02/-0mm larger than the standard dimensions when manufacturing the internal thread M13.2×0.3-6H. Then, the threads need to pass the inspections of the enlarged customized M13.2×0.3-6H +0.02/-0mm plug gauge before plating. After plating, the internal threads need to pass the inspections of a standard M13.2×0.3-6H plug gauge. Once they pass the inspection, they can be approved for shipment. If there is an external thread on the plated component, after CNC processing, the pre-plated ring gauge inspection will be necessary. And then, the inspection of a standard ring gauge should then be conducted.


What we can do without pre-plated gauges?

However, the customized pre-plated plug/ring gauges are all expensive, which are only needed for components that demand extremely high precision, but not for all components. With the long time CNC manufacturing experience, APPORO suggests to use NO GO of the standard thread gauge for the inspection criterion for threads before plating. That is, the threads could perfectly screw in the NO GO of the standard thread gauge without loosing. After plating, the threads have to pass the standard thread gauge inspections, a.k.a. GO and NO GO inspections.

This inspection is more available for components with plating film under 5um thickness. For components with plating film over 5um thickness, as its plating is for anti-corrosion purpose, and the precision requirement of it is usually lower. Even the ready made standard screws and nuts can be the inspection tools. Or, before plating the threads should be able to screw in the NO GO of the standard thread gauge but slightly loose. And then, the threads should pass the GO and NO GO inspections after plating.


When it comes to manufacture pre-plated thread, we have to leave some room for plating during CNC processing.
To use NO GO of the standard thread gauge for the inspection criterion for threads before plating. After plating, the threads have to pass the standard thread gauge inspections.


Plating and thread making are common techniques when speaking of CNC manufacturing components. Before and after different procedures, the concern will also be different. APPORO has devoted long time and and much efforts to CNC processing techniques, systematically learning from the processing experience in this field and turning it into application to increase the manufacturing efficiency and yield rates. Should you have any technical questions relevant to controlling size before/after plating, do not hesitate to contact us.


Learn more about thread gauge measurement:
Thread Gauge for instant measurement

Thread Gauge for instant measurement

So far, most of CNC machining service cases are including inner or external thread machining at APPORO. The reason for CNC machining parts featured with thread is mainly for assembly. However, there are lot’s of different thread specs for various industrial application purpose. For example, ISO Metric Standard, Unified Thread Standard, National pipe thread, British standard pipe thread, Acme thread, etc. Actually, there are various methods for verifying the quality of machined thread, such like three wire method, thread gauge. For fast and instant measurement, we prefer thread gauge which can be generally two types. One is ring gauge for inspecting external thread and the other one is plug gauge for inspecting inner threaded hole. Both these two types are supplied with Go and No Go gauges to check if the thread against its allowed tolerances.

Why we use thread gauge?

The thread gauge can literally ensure interchangeability of precision machined parts between different manufacturing procedures in CNC precision machined components industry.

After drilling a threaded hole or machining an external thread on precision CNC part, we usually use gauges for instant checking if we manufacture the thread properly and precisely. Below shows the two gauges we mainly used at APPORO-CNC:


This type of thread gauge is for inner thread measurement purpose.
Plug thread gauge


Plug gauge is for inner thread measurement purpose. As for ISO metric standard, we generally use both 6H and 6G grade for thread inspection. Each plug gauge is with two threaded ends, Go and No Go. Inner thread situations:

1.) Go doesn’t go: inner threaded hole too small or wrong pitch

Do take notice of this situation! Inner thread too small or with wrong pitch can result in assembly problem or field failures.

2.) No Go but go: inner threaded hole too big

You can take Use As It(UAI) action for this situation if the inner thread still work with mating part without functional issue. Do improve current process to eliminate this issue for long term production.


This type of thread gauge is for external thread verification.
Ring thread gauge


Ring gauge is for external thread measurement purpose. We generally use both 6h and 6g grade for ISO thread inspection. Each set of ring gauge is with two components, Go and No Go. External thread situations as below:

1.) Go doesn’t go: external thread too big or wrong pitch

Do take notice of this situation! Inner thread too big or with wrong pitch can result in assembly problem or field failures.

2.) No Go but go: external thread too small

You can take Use As It(UAI) action for this situation if the inner thread still work with mating part without functional issue. Do improve current process to eliminate this issue for long term production.



How a thread gauge works?

To fit the gauge into or onto the thread of CNC fabricated workpiece. A thread gauge cannot feedback an actual size or measurement from inspection., instead, it feedback a status which is either acceptable or unacceptable. A CNC precision manufacturing part to be acceptable via thread gauge testing means the thread within tolerance, vise versa.


If needed, we also provide customized gauges order for both plug gauge and ring gauge. Contact us to get your own thread gauges, and keep your production lines running smooth without incorrect thread fitting. Let us know about your inquiry including thread spec details for prompt machining service. You can also bound for Wikipedia for more understanding about screw thread.


Reader’s Letter:

Hi Steven,

I am a mechanical engineering student. I was going through some case studies on functional gauge and i came across the article on case study of Thread gauge in your website. I was curious to know how much money can be saved using a thread gauge on an average and some of the companies that use these thread gauge to ensure tolerance limit of the product. So could you please give me some insight on these information?.

Thanks and Regards.


APPORO’s Reply:


Thread gauge is kind of aid for quality inspection, but not for saving production cost from manufacturing. However, to use standard thread gauge for inspection is a must for being a responsible supplier and also the best way to make sure steady thread quality.

For your reference, customized thread gauges which are not commonly used might be at least 3 times to the price of general gauges. The bigger the size of the thread, the more expensive the thread gauge.

Best regards,

Cross Knurling Profile DIN 82-RGV

Standard specification of DIN 82 (link)


After CNC fabrication processing, the workpiece is usually with smooth metal surface. Knurling is a manufacturing process to feature straight, crossed, angled, diamond-like lines or pattern onto the CNC components. Generally speaking, knurling can perform better grip for finger/hand operation, plastic injection insert or decoration purpose. Sometimes, we also machined multiple shallow slots or polygonal for same above purpose. DIN 82 is most commonly used knurling spec in CNC turning machining field. For example, DIN 82-RGV is with cross knurling pattern. DIN 82-RBR/RBL is with right/left hand spiral. DIN 82-RGE is with diamond-like 30° cross male knurling.


Failure Cross Knurling

Our Belgium textile industrial customer had sent us the original sample made of stainless steel 304. The sample made by Belgium local prototyping manufacturer was with failure knurling surface. See the shorter item in below photo. The measurement of sample was precise and within tolerance, but with bad knurling which was with improper length, too light pattern, and also lack of lead in chamfer at the threaded hole.

Cross Knurling DIN 82-RGV
Cross Knurling DIN 82-RGV Compare Zoom-in


The improper length of knurling do bad for its appearance, a customized full length cross knurling tool can solve this issue. Too light patter may result from the CNC programming or limitation of CNC lathe. Moreover, our CNC production lines can easily machine the lead in chamfer on the edge of threaded hole.

Improved knurling

Therefore, we ordered a customized full length knurling tool to meet the required pattern spec of DIN 82-RGV 0.8. An automatic Japaneses CNC turn-mill machine also helps improving the quality of surface and dimensions. Above photo shows the longer workpiece machined by APPORO is with improved knurling pattern.


We can offer CNC precision parts with several types of knurling surface, such like straight knurling, cross knurling, diamond-like knurling. Our production lines are also capable of knurling on precision plastics parts. Should you have any inquiry for above knuring surface on your CNC workpieces, kindly send us RFQ for free project reviewing without hesitation.