-- The Home Page of the Finishing Industry

on this site
current topics
Live! From beautiful Pine Beach New Jersey: Welcome to the world's most popular metal finishing website

topic 7560




Michael L [last name deleted for privacy by Editor]
-Wyandotte, Michigan


A. Grade Numbers Older drawings may use roughness grade numbers to indication Ra values. The following table is given in ISO 1302 [info about this spec at Amazon; and at Techstreet]

Roughness values Ra Roughness values Ra Roughness
micrometers microinches Grade Numbers
50 2000 N12
25 1000 N11
12.5 500 N10
8.3    6.3 250 N9
3.2 125 N8
1.6 63 N7
0.8 32 N6
0.4 16 N5
0.2 8 N4
0.1 4 N3
0.05 2 N2
0.025 1 N1

Good Luck.

Bill Boatright
-Raleigh, North Carolina


thumbs up signHi,

I like your table. However, I believe there's a small mistake. The metric value corresponding to a 250 micro-inch surface roughness/finish should be 6.4 micrometers, rather than 8.3.

Best regards,

Justin H [last name deleted for privacy by Editor]
pressure vessels - Erie, Pennsylvania


Q. Bill,

Great chart! Is this a new ISO standard for all metal surfaces?


Michael Liu Taylor
Michael Liu Taylor
   specialty stainless steel distributor
Dallas, Texas



Q. One of our Customer Drawings indicate a Surface Finish specification of N6.

We only have a Surface Finish Tester that can measure Rz & Ra.

Where Can I find or how do I convert N to Rz?

Henry R [last name deleted for privacy by Editor]
automotive engineering - Benoni, Gauteng, South Africa

A. Hi, Henry. You can see that the chart tells you N6 = Ra of 32 microinches. So your test device which measures Ra should work.

If you search the site for "Ra vs Rz" you will see that while they tend to track each other, they are not directly equivalent.

Sort of like small engines produce little torque or horsepower, and large engines produce a lot of torque and horsepower, but you simply can't convert torque to horsepower because it's not the same thing.


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


Q. I am trying to find out what a 63u finish is? I have put this finish on a polycarbonate part that needs to be machined.
Thank you for your help.

Bruno D [last name deleted for privacy by Editor]
machining - Melbourne, Florida

April 23, 2008

A. Hi, Bruno. I think most people would take this to be 63 microinch finish. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

April 23, 2008

Q. Hi
I'm a student and have a confusion that which is a better surface finish of these two
N5 or N10 ?

Waqas Alam
UET - Taxila, Pakistan

May 2008

A. Hi, Waqas. In the chart above, rougher finishes are at the top and smoother finishes are at the bottom.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

June 22, 2010

Q. Hello Sir!

My name is Emre Özcan, I'm 24 years old, metallurgical and materials engineer at a machinery shop at Turkey.I am also a MSc. Student. We have a little troubleshooting about the interpretation of a roughness value on a technical drawing that came from one of our customers.

While I was searching for answers regarding this problem, I have seen your article on the website and I have got your e-mail from this website. I decided to consult this problem to you and I'm wondering if you can help me out in this problem?

The problem is simple: We have a furnace roll on the technical drawing, and the surface roughness value of this roll is represented with "CRODAN #3" or "CRDDAN #3".This is the surface roughness value of grounded and sandblasted condition of the piece. We have no idea what CRODAN #3 is. Can you tell us the Ra equivalent of this value?

Thanks in advance,

Emre Ozcan
- Ankara, Turkey

July 5, 2010

Q. The table above is in our SABS 0111 - Engineering Drawing Standard, but how do we relate the numbers to a physical finish or machining method? I.e., what code for a standard turning finish, a good milling finish or for a ground and polished finish)

William Jackson
- Durban, South Africa

January 16, 2012

Q. MPc. I have a surface condition of 12S. What does it mean and how does it convert to 118 Ra?

Hector G.
- Chicago, Illinois

January 17, 2012

Apologies, Hector, but I have to say: "What?!"

I'm not familiar with "MPc" in this context, nor with "12S" in this context, nor with what you even mean by "convert to 118 Ra". Sorry.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

February 6, 2012

Q. Can anybody tell me how the ISO surface finish is used on a drawing?

Thank you all!

Kevin Kaminski
- Dublin, Ohio, United States

April 9, 2015

Q. I have a customer looking for a finish of " UOS-125AA". I can't find it.

Dennis Kimball
- Auburn, Massachusetts USA

April 2015

A. Hi Dennis. When you google something like that and you come up empty it means it doesn't have a universally accepted meaning, and you'd better talk to your customer or there's a good chance there could be trouble brewing :-(

My guess is that it means "unless otherwise stated, all surfaces are to be finished to 125 arithmetic average", but if an unhappy customer complains that you didn't build it to Ubiquitous Ostriches Standard 125 As Amended, it will be your fault rather than theirs :-)


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

If you have a question in mind which seems off topic, please Search the Site

ADD a Q, A, or Comment on THIS topic START an UNRELATED topicView CURRENT HOT TOPICS

Disclaimer: It's not possible to 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 may be deliberately harmful.

  If you need a product/service, please check these Directories:

JobshopsCapital Equip. & Install'nChemicals & Consumables Consult'g, Train'g, SoftwareEnvironmental ComplianceTesting Svcs. & Devices

©1995-2019, Inc., Pine Beach, NJ   -   About   -  Privacy Policy
How Google uses data when you visit this site.