Stainless steel 4B finish specifications
Q. Our company supplies stainless steel equipment for the food industry but typically use mill finish products without any special polishing. I was asked on a recent project to supply a 4B finish. I see a lot of equipment specified this way and most of the stainless suppliers describe a #4 finish as 150-180 grit polish. Does anyone know if there is 4B different from #4, and is there a 4A finish?Dan Cooper
- Roscoe, Illinois
A. There is no relationship between a #4 (dairy) finish and a 4B mill finish. The #4 finish is a ground finish. There is little agreement on what it should look like and you will rarely find two #4 finishes that look or feel the same though the surface roughness numbers (Ra's) will be broadly similar. A 4B mill finish is produced by rolling the sheets of stainless steel between polished rollers. It commonly has a slightly matte or frosted appearance. The surface is usually very smooth but the Ra's can be all over the place and still meet the spec.. I did a survey of mills a few years back and got readings from 8 to 28 Ra. We most commonly see Ra's in the range of 8 to 20. Is there a 4A finish? It seems logically consistent but I must confess, I don't know.John Holroyd
- Elkhorn, Wisconsin
May 12, 2008
A. To the best of my understanding there is no 4B finish.
Over time people have somehow combined a 2B and a #4 finish.And incorrectly called it a 4B finish.
Most of the time when referring to a 4B finish they actually want a #4 finish.
Sometimes however when referring to a 4B finish they want a #2B finish.
Its best to talk to them so you understand what they want.
Check out "Wikipedia" under "stainless steel finishes"
it list and explains industry standard finishes.
- Traverse City, Michigan
February 12, 2010
A. The previous response is correct. There is no "4B" finish recognized by ASTM and a colleague confirmed that there is no industry specific 4B. The relevant ASTM standard for stainless steel sheet and strip finishes is ASTM A480 [link by ed. to spec at TechStreet]. Another potential source of confusion is that the Europeans and Japanese have two No. 4 finishes. The difference between them is surface roughness and surface roughness maximums are not uncommon in industry.Catherine Houska
consulting - Pittsburgh, Pennsylvania
March 21, 2011
A. I do not understand why we call it 4B Finish as it is not mentioned in any Technical Standards Books related to Stainless Steel Surface Finish. If any such Code is available let me Know. But as far as I understand no such Code called 4B Finish exists.
Can anybody explain me with details about 4B Finish with Photograph?
Indian Institute Of Technology - Pune, Maharashtra, India
March 5, 2012
A. The web site below gives an explanation of a "4B Dairy Finish":
Massman - Villard, Minnesota, usa
Ed. note: July 2018. Although that page is now gone, you can view it courtesy of the Internet Archive:
July 14, 2018 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. I'm trying to decide, for a deck rail project, the difference between a mill finish and a 180 grit finish. Which is more costly? Would someone please explaing. g. gurbuz
restorer - Etowah North Carolina, USA
A. Hi G.G.
Can we assume you are speaking of stainless steel railings?
A "mill finish" means no finishing after rolling at the steel mill. It's probably somewhat smooth from rolling, but few guarantees about anything. A 180-grit finish is probably a scratch-brush finish from passing through a machine which scratches it with an endless belt of 180-grit sandpaper.
The extra operation probably costs some amount of money. But you ought to be able to see samples rather than buying a pig in a poke. Good luck.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Striving to live "Aloha"
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