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| + | ====== Grade Marks and Material Properties for Bolts and Screws ====== | ||
| - | ===== Strengths Of Various | + | Bolts, screws and other fasteners are marked on the head with a symbol that identifies the grade of the fastener. ((Machinery' |
| + | The grade specification establishes the minimum mechanical properties that the fastener must meet. \\ | ||
| + | Additionally, | ||
| + | The grade identification table identifies the grade markings and gives mechanical properties for some commonly used ASTM and SAE steel fasteners. \\ | ||
| + | Metric fasteners are identified by property grade marks, which are specified in ISO and SAE standards. \\ | ||
| + | These marks are discussed with metric fasteners. | ||
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| + | ====== Mechanical Properties and Grade Markings of Nuts ====== | ||
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| + | Three grades of hex and square nuts designated Grades 2, 5, and 8 are specified by the SAE 1995 standard covering nuts in the 1/4" to 1-1/2" diameter range. ((Machinery' | ||
| + | Grades 2, 5, and 8 nuts roughly correspond to the SAE specified bolts of the same grade. \\ | ||
| + | Additional specifications are given for miscellaneous nuts such as hex jam nuts, hex slotted nuts, heavy hex nuts, etc. \\ | ||
| + | Generally speaking; use nuts of a grade equal to or greater than the grade of the bolt being used. \\ | ||
| + | * Grade 2 Nuts: | ||
| + | * Grade 2 nuts are not required to be marked. | ||
| + | * Grade 5 Nuts (1/4" to 1-1/2" range): | ||
| + | * A dot on the face of the nut and a radial or circumferential mark at 120° counterclockwise from the dot. | ||
| + | * Or a dot at one corner of the nut and a radial line at 120° clockwise from the nut. | ||
| + | * Or one notch at each of the six corners of the nut. | ||
| + | * Grade 8 Nuts (1/4" to 1-1/2" range): | ||
| + | * A dot on the face of the nut with a radial or circumferential mark at 60° counterclockwise from the dot. | ||
| + | * Or a dot at one corner of the nut and a radial line at 60° clockwise from the nut. | ||
| + | * Or two notches at each of the six corners of the nut. | ||
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| + | ====== Detecting Counterfeit Fasteners ====== | ||
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| + | Fasteners with markings identifying them as a specific grade or property class are counterfeit if they don't meet standards established for that class. ((Machinery' | ||
| + | Counterfeit fasteners may break unexpectedly at smaller loads than expected. \\ | ||
| + | Generally, these fasteners are made from the wrong material or they are not properly strengthened during manufacturing. \\ | ||
| + | Either way, counterfeit fasteners can lead to dangerous failures in assemblies. \\ | ||
| + | The law now requires testing of fasteners used in some critical applications. \\ | ||
| + | Detection of counterfeit fasteners is difficult because the counterfeits look genuine. \\ | ||
| + | The only sure way to determine if a fastener meets it's specification is to test it. \\ | ||
| + | However, reputable distributors will assist in verifying the authenticity of the fasteners they sell. \\ | ||
| + | For important applications, | ||
| + | Typical lab checks used to detect fakes include testing hardness, elongation, ultimate loading and a variety of chemical tests. \\ | ||
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