In this article, I will introduce what 2B, BA, No. 4, hairline and mirror finishes are, how each one is made, when a buyer specifies each finish, and what to send so two offers describe the same surface.
What the finish names mean
A finish is the surface, not the alloy. A 304 sheet in 2B and a 304 sheet in No. 4 are the same grade and different orders. The grade is what a mill test certificate is checked against. The finish is what the eye, and a sample, are checked against.
On flat products the names buyers write most often are No. 1, 2B, BA, No. 4, hairline (HL), and a mirror written as No. 8 or as the trade name 8K. ASTM A480 is the usual US document for these sheet and plate finishes. EN 10088-2 uses its own codes, including 2B, 2R, 2K and 2P. A name from one standard can be discussed next to a name from the other. It is not an automatic substitution. The standard printed on the drawing is the one to quote.
How each finish is produced
No. 1 is hot-rolled, annealed and descaled. The surface is dull, and it is the usual industrial plate face. It is not a decorative skin. If the part will be seen, No. 1 is the wrong line unless the drawing asks for it.
2B is cold-rolled, annealed, pickled and then skin-passed, a light roll on polished rolls. It is smooth and moderately reflective. It is the general-purpose mill finish for cold-rolled sheet and coil. It is not a brush, and it is not a mirror. 2D is the duller cold-rolled finish. It is not skin-passed on polished rolls the way 2B is. If the drawing says 2D, do not replace it with 2B.
BA is bright annealed. The metal is annealed in a controlled atmosphere so the surface is not left dull by oxidation, and it is often given a light roll afterward. It is brighter than 2B. EN 10088-2 type 2R is the bright-annealed finish buyers set beside BA. Keep the name the drawing prints. BA is still a mill finish. It is not a mirror made by abrasives.
No. 4 is a directional polish. ASTM A480 describes it as a general-purpose polished finish produced with abrasives of about 120 to 150 grit. The grain is visible. One side is the usual polished face unless the order says both sides. When panels meet, the grain direction is part of the order.
Hairline, often written HL, is also a directional brush. In export orders the lines are generally finer than a No. 4 grain. HL is a commercial name. It is not an ASTM A480 number, and the grit is not fixed by that text. Two mills can both say hairline and still look different. On a visible job, an approved sample is how the surface is matched. A No. 4 sheet and an HL sheet of the same grade are not the same order.
No. 8 is a mirror under ASTM A480, made by successive polishing and buffing. Grit lines are not readily visible. 8K is the commercial name many export offers use for a mirror. 8K is not an ASTM designation. If the drawing says No. 8, the offer should say No. 8. If the drawing says 8K, the offer should say 8K. Where both names appear on one enquiry, a sample settles the visible face.
Pipe and bar do not take the sheet list unchanged. A pipe surface is more often written as polished, hairline or mirror under the pipe standard. A round bar is more often pickled, bright or polished. Copy the words the drawing uses for that form. A 2B line does not replace them.
What naming the finish protects
The finish decides which process is run, and how the part will look when it arrives. The grade does not decide it.
A mill finish the shop can use
No. 1, 2B and BA leave the mill as a surface, not as a brushed or mirrored face. A fabricator who expected 2B and received No. 4 has a different job, and the reverse is also true. Protective film, when a job needs it, is there for transit. The film is not the finish. If the face must stay covered until installation, write the film as its own line.
A grain the panels can share
No. 4 and hairline have a direction. On a cabinet, a wall or a run of doors, the grain has to run the same way. Write that direction when the panels are visible and they meet. A mirror has no grain. Do not describe a mirror as hairline, and do not describe hairline as a mirror.
One offer that can be set beside another
Two quotes match only when both name the same finish, the same standard, and whether one side or both sides are finished. A polished face is often one side. The back may stay 2B. If the drawing is silent, ask. Do not assume both sides. A photograph is not a finish code.
When each finish is the one to order
Order No. 1 when the drawing names it for hot-rolled plate that will be cut or welded and the face is not decorative. Order 2B when the drawing names the common cold-rolled mill finish for equipment, tanks and parts that are not a show face. Order BA when the drawing asks for a bright mill finish, such as an appliance skin or a reflective panel that is not a mechanical mirror.
Order No. 4 or hairline when the drawing asks for a directional brushed face. Keep the name it uses. Do not swap them to skip a process. Order No. 8 or 8K only when the drawing asks for a mirror, and keep that name as well. Do not upgrade 2B to No. 4 because a photo looks brighter. Do not downgrade a mirror to BA to lower the price unless the end user agrees. A finish change is not a grade change. 304 stays 304, and 316 stays 316.
Embossed sheet, water-wave sheet and colored sheet are separate forms. They are not finish codes in ASTM A480. If the drawing names one of those forms, the enquiry should name it. Do not fold it into 2B or No. 4.
2B versus BA versus No. 4 versus hairline
2B and BA can share a grade, a thickness and a width and still be different surfaces. One is pickled and skin-passed. The other is bright annealed. BA is brighter. Neither is brushed.
No. 4 and hairline are both directional brushes, and they are still different orders. No. 4 is the ASTM general-purpose polish. Hairline is the finer commercial brush. On a visible run, a mixed shipment is obvious. EN 10088-2 types 2J and 2K are polished finishes buyers sometimes set beside a brush. They are not automatic substitutes for No. 4 or HL.
A mirror is a further polish. BA can look bright under a lamp and still fail a mirror specification. Type 2P in EN 10088-2 is a bright polished finish, and it belongs in that conversation only when the drawing names it. If an enquiry says only polished, or only mirror finish, ask which name and which standard, or ask for the sample the end user approved.
FAQ
These are the questions that usually decide whether the first offer can be used.
Is 2B the same as a mirror?
No. 2B is a smooth, moderately reflective mill finish. A mirror is No. 8 or the trade name 8K, made by polishing. A bright lamp on 2B does not make it a mirror.
Is BA the same as 8K?
No. BA is bright annealed on the mill line. 8K is a commercial name for a mirror polish. They are different processes. A BA sheet does not satisfy an 8K line, and an 8K sheet does not satisfy a BA line.
Can hairline replace No. 4?
Only if the end user agrees. Both are directional brushes. HL is not an ASTM A480 number, and the grit is not the No. 4 grit. For a visible part, keep the name on the drawing or match an approved sample.
Does the finish change the grade?
No. The finish is the surface and the grade is the alloy. A 304 sheet in No. 4 is still 304. A 316 sheet in 2B is still 316. The certificate has to match the grade and the product standard. The finish is checked against the order and, on a visible part, against the sample.
Does one side or both sides matter?
Yes. Decorative polishing is often one side. Write one side or both sides. If the back of a panel will be seen, both sides have to be on the enquiry. A one-side polish with a 2B back is a normal order only when that is what the drawing allows.
Can a pipe be ordered as 2B?
Not by copying a sheet line. Sheet finishes and pipe finishes are specified differently. A pipe order names the pipe standard and the surface that drawing uses, such as polished, hairline or mirror. The sheet code does not replace that line.
What to send with the enquiry
Write the form first, then the grade and the product standard, then the finish in the words the drawing uses: No. 1, 2B, 2D, BA, No. 4, HL, No. 8 or 8K. Add one side or both sides, the grain direction if the face is brushed and the panels meet, the size and the quantity. If the job is visible, send the approved sample or say that a sample is required before the finish is run. Sheet, coil and pipe are confirmed as separate lines. The finish is confirmed with them. It is not assumed from a photograph.