Stainless Reference Tables
The numbers we use across this site, in one place, with the convention behind each one stated so you can check it.
Grade reference, 18 grades
Composition limits, PREN as a range and as a typical figure, machinability, weldability and what each grade is actually specified for.
Standards on a stainless drawing, 16 of them
ASTM, AMS, ISO and 3-A callouts you will meet, what each one governs and when to name it.
Grade selector
Five questions about the environment and the duty, and a grade with the reasoning shown. Runs in your browser.
PREN calculator
Pitting resistance from composition, with the machinability trade-off shown next to it.
The conventions used here
Two numbers do most of the work on this site, and both are easy to misread if the basis is not stated.
PREN, the pitting resistance equivalent number, is chromium plus 3.3 times molybdenum plus 16 times nitrogen, taken from the composition. It orders grades by how well they resist chloride pitting. It is not a corrosion rate and it says nothing about stress corrosion cracking or crevice attack.
Machinability is rated against free-machining carbon steel B1112 at 100. Published ratings differ by a few points between sources because they come from different test conditions. Treat the number as an ordering, not as a measurement.
Everything on these pages describes the alloy. None of it is a promise about your geometry or about any shop. The reasoning behind that split is on the about page.