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| THE BASIC TEMPER DESIGNATIONS | |
| Letter | Meaning |
| F | As fabricated – Applies to products of a forming process in which no special control over thermal or strain hardening conditions is employed |
| O | Annealed – Applies to product which has been heated to produce the lowest strength condition to improve ductility and dimensional stability |
| H | Strain Hardened – Applies to products that are strengthened through cold-working. The strain hardening may be followed by supplementary thermal treatment, which produces some reduction in strength. The “H” is always followed by two or more digits |
| W | Solution Heat-Treated – An unstable temper applicable only to alloys which age spontaneously at room temperature after solution heat-treatment |
| T | Thermally Treated - To produce stable tempers other than F, O, or H. Applies to product that has been heat-treated, sometimes with supplementary strain-hardening, to produce a stable temper. The “T” is always followed by one or more digits |