Mechanical Polishing
Andron Stainless provides the industrial array of precision polishing and finishing for sanitary stainless steel products. Within various industries related to metal working, polish terminology varies causing considerable confusion. This information is meant to define and outline our interpretation of these different polish terms.
Polish Combinations
1 - Unpolished
3 - Polished on the inside only or ID
5 - Polished on the outside only or OD
7 - Polished on both the inside/outside or ID/OD
304/304L Standard Polished Finish 32Ra ID / 32Ra OD
316/316L Standard Polished Finish 25Ra ID / 32Ra OD
When calling out a polish type on our coding system, it is defined as a polish combination. There are four different polish combinations.
We determine our polish finish using the Ra scale. Ra is defined as roughness average and is the most accurate measure of surface finish roughness. We measure the Ra using a surface roughness tester or profilometer. Often times the desired level of polish is called out in terms of grit. Below is a chart to cross reference grit to Ra.
| Ra µin / µm |
Grit |
Rms µin / µm |
| 43 - 48 / 1.09 - 1.22 |
120 |
48 - 54 / 1.22 - 1.37 |
| 30 - 35 / .76 - .89 |
150 |
34 - 39 / .86 - .99 |
| 23 - 28 / .58 - .71 |
180 |
26 - 32 / .66 - .81 |
| 15 - 20 / .38 - .51 |
240 |
17 - 23 / .43 - .58 |
| 9 - 13 / .23 - .33 |
320 |
10 - 15 / .25 - .38 |
Often used is the biopharm industry codes. These codes are also defined below.
| Surface Finish Code |
ID / OD Finish (Maximum Ra Allowed) |
BPE Designation |
| PX |
Unpolished / Unpolished |
SF0 |
| PZ |
Unpolished / 32 Ra |
SF0 |
| PC |
20 Ra Mechanical / Unpolished |
SF1 |
| PF |
25 Ra Mechanical / Unpolished |
SF2 |
| PB |
30 Ra Mechanical / Unpolished |
SF3 |
| PL |
20 Ra Mechanical / 32 Ra |
SF1 |
| PT |
25 Ra Mechanical / 32 Ra |
SF2 |
| PQ |
30 Ra Mechanical / 32 Ra |
SF3 |
| PD |
15 Ra Mechanical & Electropolished / Unpolished |
SF4 |
| PG |
20 Ra Mechanical & Electropolished / Unpolished |
SF5 |
| PK |
25 Ra Mechanical & Electropolished / Unpolished |
SF6 |
| PM |
15 Ra Mechanical & Electropolished / 32 Ra |
SF4 |
| PO |
20 Ra Mechanical & Electropolished / 32 Ra |
SF5 |
| PO |
25 Ra Mechanical & Electropolished / 32 Ra |
SF6 |