Three radial marks on a bolt head indicate imperial grade 5.

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Multiple Choice

Three radial marks on a bolt head indicate imperial grade 5.

In imperial fasteners, the head markings show the strength grade, with the number of radial lines serving as a quick visual code. Three radial marks indicate a mid‑strength bolt known as Imperial Grade 5. This makes sense because Grade 5 sits between the lower Grade 2 (which typically has little to no head markings) and the higher Grade 8 (which uses six radial lines). Knowing this helps you quickly assess suitability: a bolt with three lines is Grade 5, not Grade 2 or Grade 8. Metric bolts, and some SAE designs, use different marking schemes (like numeric suffixes such as 8.8 or other symbols) rather than radial lines, so they wouldn’t display three radial marks.

In imperial fasteners, the head markings show the strength grade, with the number of radial lines serving as a quick visual code. Three radial marks indicate a mid‑strength bolt known as Imperial Grade 5. This makes sense because Grade 5 sits between the lower Grade 2 (which typically has little to no head markings) and the higher Grade 8 (which uses six radial lines).

Knowing this helps you quickly assess suitability: a bolt with three lines is Grade 5, not Grade 2 or Grade 8. Metric bolts, and some SAE designs, use different marking schemes (like numeric suffixes such as 8.8 or other symbols) rather than radial lines, so they wouldn’t display three radial marks.

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