HELICAL COIL SCREW THREAD INSERTS Machinery's Handbook, 31st Edition
1746
PLUG STYLE TAP
BOTTOMING STYLE TAP
T
G
2 Pitch incomplete threads 1 Pitch tap end clearance
4 Pitch incomplete threads
1 Pitch tab end clearance
Fig. 1. Tapping Depth Designation for STI-Threaded Hole Including Installed Helical Coil Insert: The drawing note for the STI-threaded hole per Table 1 having a helical coil insert installed shall be in accordance with this example. Example 3: M8 × 1.25 STI 23.5 deep; Helical Coil insert, ANSI/ASME B18.29.2M, M8 × 1.25 × 12.0, free running Gages and Gaging: Acceptance of the threaded hole is determined by gaging with STI GO, NOT GO (HI), and plain cylindrical gages designed and applied in accordance with System 21 of ANSI/ASME B1.3 and with ANSI/ASME B1.16M. Helical Coil Insert Material.— Chemical composition of the inserts is austenitic corrosion-resistant (stain less) steel material within the limits of Table 2. Properties.— Wire, before coiling into inserts, shall have tensile strength not lower than 1035 MPa, determined in accordance with ASTM A370. Wire shall withstand, without cracking, bending in accordance with ASTM E 290 at room temperature through an angle of 180 ° around a diameter equal to twice the cross-sectional dimension of the wire in the plane of the bend. The formed wire shall be of uniform quality and temper; it shall be smooth, clean, and free from kinks, waviness, splits, cracks, laps, seams, scale, segrega tion, and other defects that may impair the serviceability of the insert. Coatings.— At the option of the user, dry film lubricant coating can be applied to helical coil inserts.The color of dry film-lubricated inserts is dark gray to black. Lubricant shall meet requirements of Aerospace Standard SAE AS5272, type I, lubricant, solid film heat cured, and corrosion inhibiting. Coating shall be uniformly deposited on the insert with the minimum thickness being complete coverage. Maximum thickness shall be the avoidance of bridging between coils. Slight fill in between closely wound coils, which immediately separates as the coils are axially pulled apart by hand, shall not be considered bridging. Configuration and Dimensions.— Insert configurations shall be in accordance with Fig. 2 , and dimensions shall be in accordance with Table 3 and Table 4. Each nominal insert size is standardized in five lengths, which are multiples of the insert’s nominal diameter. These are 1, 1.5, 2, 2.5, and 3 times nominal diameter. Each nominal length is the minimum through-hole length (material thickness), without countersink, into which that insert can be installed. The nominal insert length is a reference value and cannot be measured. Actual assembled length of the insert equals nominal length minus 0.5 pitch to minus 0.75 pitch, with insert installed in a basic STI threaded hole. Assembled length cannot be measured in the insert’s free state.
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