The bar, forging, heat treatment, machining and handling can all leave marks on a fastener. Within their limits many do no harm; in the wrong place, none are allowed, so each mark is named and judged by where it is as well as by its size. For bolting in dynamic service, ASTM A962 allows no quench crack of any size, no fold at the junction of head and shank and no thread lap at the root or below the pitch line.
For ASTM bolting the limits come in through the specification. A193, A194 and A320 rely on ASTM A962, which requires bolts and studs to be capable of passing inspection to F788, and nuts to F812; A449, A354, A307 and F3125 call F788 directly. Magnetic particle inspection, or penetrant on stainless and nickel alloys, shows a mark's full length when a closer look is needed.
Read the full surface discontinuity inspection page →
model dataThe bolt is drawn to scale: a 1 in. ASTM F3125 Grade A490 heavy hex structural bolt, 6 in. long; the nut is a 1 in. ASTM A194 2H heavy hex nut. Every mark is illustrative and drawn larger than life, and the thread profile is magnified. Types of discontinuity from ASTM F788 and F812; the seam and thread-lap limits quoted are those of ASTM A574; magnetic particle testing of sample A490 bolts, and the microscope or grinding check of an indication's depth, from ASTM F3125 and A354; UV-A of at least 1000 µW/cm² at the part as cited from ASTM by a UV-A meter maker; no quench cracks in bolting for dynamic service from ASTM A962; the cone proof load test and its load for this nut, 74,200 lbf on a 120° cone, from ASTM A194, A962 and F606. The magnetising shot is shown slowed down and the cut sped up.
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