ASME B18.29.2M pdf download Helical Coil Screw Thread Inserts: Free Running and Screw Locking (Metric Series)
For definitions of terms relating to fasteners or compo-nent features thereof used in this Standard, refer toASME B18.12
(a)Unless otherwise stated, all dimensions in thisStandard are in millimeters and apply before any coat-ing. When plating or coating is specified, the finishedproduct dimensions shall be as agreed upon by the supplier and purchaser.
(b)Symbols specifying geometric characteristics arein accordance with ASME Y14.5M.
Helical coil inserts are screw thread bushings coiledfrom wire of diamond-shape cross-section. Inserts arescrewed into STI-tapped holes to form nominal sizeinternal threads. Inserts are installed by torquingthrough a diametral tang. This tang is notched forremoval after installation. In the free state, they are largerin diameter than the tapped hole into which they are installed.In the assembly operation, the torque appliedto the tang reduces the diameter of the leading coil andpermits it to enter the tapped thread. The remainingcoils are reduced in diameter as they, in turn, are screwedinto the tapped hole. When the torque or rotation isstopped, the coils expand with a spring-like actionanchoring the insert in place against the tapped hole
7 CLASS OF FIT
71 Tolerance Classes 4H5H and 5HSince helical coil inserts are flexible the class of fit ofthe final assembly is a function of the size of the tappedhole. Helical coil STI taps are available for both ToleranceClass 4H5H- (or Class 4H6H- ) and Class 5H- tappedholes.Tolerance Class 5H- tapped holes provide maxi-mum production tolerances but result in lower lockingtorques when screw-locking inserts are used. The higherand more consistent torques qiven in Table 5 are metby the screw-locking inserts when assembled and testedin Tolerance Class 4H5H (or Class 4H6H- ) tapped holesin accordance with para.9
Assembled helical coil inserts will mate properly withitems that have M Profile external threads in accordancewith ASME B1.13M. Also, due to the radius on the crestof the insert at the minor diameter, the assembled inserwill mate with MJ Profile externally threaded parts withcontrolled radius root threads per ASME B1.21M
8 TYPES OF INSERTS
8.1 Free-RunningThe free-running insert provides a smooth, hard, andfree-running thread.
The screw-locking insert provides a resilient lockingthread produced by a series of chords on one or moreof the insert coils.
The tapped hole into which the insert is installed shallbe in accordance with ASME B113M.except that diame-ters are larger to accommodate the wire cross-section ofthe insert (see Fiq.1). Dimensions of the STI-tapped holeare shown in Table 1 and are calculated per GeneralNote (c) to Table 1.
9.1 Screw Thread Designation9.1.1 Designation for Tapped Hole. The drawing notefor the STI-threaded hole per Table 1 to accept the helicacoil insert shall be in accordance with the followingexample:
EXAMPLE: M81.25-5H STI 23.5 per ASME 818.29.2M