ASTM A962, which A193, A194 and A320 call up, requires the grade symbol and the manufacturer's identification on one end of studs 3/8 in. (10 mm) and larger, on the heads of bolts 1/4 in. (6 mm) and larger, and on every nut whatever its size. Bolts are marked on top of the head, never on the bearing face; A194 nuts on one face, not the wrench flats.
The symbol says more than the grade: A194 adds a B to nuts machined from bar (2HB) and an L to nuts impact tested for low temperature (7L). The heat code alongside ties each part to its material test report, and through it to the mill certificate for that heat.
Read the full dot-peen marking page →
model dataWhere the marks go: ASTM A962 (studs 3/8 in. and larger on one end, bolt heads 1/4 in. and larger, never the bearing surface, every nut) and ASTM A194 (one face of the nut, the grade symbol showing how it was made). Round-bottomed low-stress marks against the sharp V of ordinary stamps: MIL-STD-792 as summarised in published fatigue research. The pin is carbide-tipped, driven by a pulsed coil or by air, and returns after each stroke. The stud is drawn as a 1-1/4-8 UN B7 stud and the bolt and nut to 1 in. heavy hex proportions (ASME B18.2.1 and B18.2.2). The maker's mark is INF, marked above the grade symbol with the heat code below (on a nut face the three are equally spaced round it), and H-24A117 is an example heat. The marking head, controller, fixture, test report and mill certificate are generic, and the documents show no results. The first stroke is slowed right down, and the section and the marked end are shown enlarged.
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