HELICAL COIL SCREW THREAD INSERTS Machinery's Handbook, 31st Edition
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In using this table, the following factors must be considered: a) The parent material shear strengths are for room temperature. Elevated temperatures call for significant shear value reductions; compensation should be made when required. Shear values are appropriate because the parent material is subject to shearing stress at the major diameter of the tapped threads. b) When parent material shear strength falls between two tabulated values, use the lower of the two. c) Bolt thread length; overall length, insert length, and full tapped thread depth must be adequate to ensure full-thread engagement when assembled to comply with its design function. Table 7. Insert Length Selection ANSI/ASME B18.29.2M-2005 (R2017) Parent Material Shear Strength, MPa Bolt Property Class 4.6 4.8 5.8 8.8 9.8 10.9 12.9 Insert Length in Terms of Diameters 70 3 3 3 … … … … 100 2 2 2 3 … … … 150 1.5 1.5 1.5 2 2.5 2.5 3 200 1.5 1.5 1.5 2 2 2 2 250 1 1 1 1.5 1.5 1.5 1.5 300 1 1 1 1.5 1.5 1.5 1.5 350 1 1 1 1 1 1.5 1.5 Table 8. Hardness Number Conversion ANSI/ASME B18.29.2M-2005 (R2017) Bolt Property Class Max. Rockwell Hardness Max. Tensile Strength, MPa Bolt Property Class Max. Rockwell Hardness Max. Tensile Strength, MPa 4.6 95 RB 705 9.8 36 RC 1115 4.8 95 RB 705 10.9 39 RC 1215 5.8 95 RB 705 12.9 44 RC 1435 8.8 34 RC 1055 Bolt strength upon which insert length recommendations are based is developed by taking the maximum hardness per ASTM F568M Carbon and Alloy Steel Externally Threaded Metric Fasteners and the equivalent tensile strength from SAE J417 Hardness Tests and Hardness Number Conversions . Screw Thread Insert Taps.— ANSI/ASME B94.9 covers design and dimensions for taps for producing Metric Series STI-threaded holes required for the installation of helical coil screw thread inserts. Threaded hole dimensions are shown in Table 1 of this standard. Helical coil screw thread insert taps are identified by the designation STI. Various types and styles of STI taps are available. General dimensions and tolerances are in accordance with ANSI/ASME B94.9. Tap Thread Limits: Ground thread taps are recommended for screw thread inserts. Tap thread limits are in accordance with ANSI/ASME B94.9. Basic pitch diameter used for determining values is the “Pitch Diameter, min.” from Table 1. Marking: Taps are marked in accordance with ANSI/ASME B94.9. Example: M6 × 1STI HS G H2.
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