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A full thread bolt with a six sided head


There can be some confusion with identifying various types of hex bolts. We will cover three types: HEX CAP SCREWS, TAP BOLTS and MACHINE BOLTS. All three are very similar looking and can be easily mistaken for one another unless you are familiar with these slight differences.


HEX CAP SCREWS


Hex cap screws are recognized by the washer faced bearing surface under the head. They are partially threaded with an unthreaded area referred to as the & quot;grip& quot;. The minimum thread length is measured as twice the diameter plus 1/4& quot; for screws 3/4& quot; in diameter up to 6& quot; long inclusive. These screws are cold form manufactured with rolled threads. When screw length is too short for the minimum thread length rule to apply, they shall be fully threaded.


Screws with a length longer than 6& quot; have a minimum thread length of twice the diameter plus 1/2& quot;. The3se larger screws may be either hot or cold headed and the threads may be cut, rolled, or ground at the manufacturer& acute;s option. Hex cap screws are available in various grades of steel.


Grade 2


Does not require a heat treatment but may require stress relief. There are no head markings on Grade 2 bolts and therefore are most likely to be confused with machine bolts. To verify check for a washer faced bearing surface under the head. Minimum tensile strength = 74Ksi.


Grade 5


Are heat treated, quenched in oil or water and tempered at 800°F. Look for the three radii markings on top of head. Minimum tensile = 120 Ksi.


Grade 8


Are heat treated, quenched in oil and tempered at 800°F. Look for the 6 radii starbu