ISO 4579:2021 pdf download – Aerospace — Drives, internal, TORX® PARALOBE® drive — Geometrical definition, gaging and technical requirements.
6.3 Driver bit The driver bit shall be appropriate for the recess being tested and shall be in accordance with the requirements of ISO 4580. 6.4 Test specimen The shank of the fastener or fastener head may be modified to ensure non-rotation during testing. The recess shall be gaged after fastener modification. 6.5 Fastener recess torque test procedure a) Place the fastener in a suitable test fixture. b) Mate the driver bit with the recess of the fastener, ensuring that the bit is free to move in or out of the recess and the bit axis is constrained within 1° of angular alignment with the fastener axis. c) Apply an end load as specified in NASM1312-25. The total end load shall be effective at bit/fastener juncture. d) With the bit mated to the recess and the end load applied (but no torque applied), zero the torque measuring device if applicable. e) Apply the torque slowly in the installation direction at a smooth, continuous rate until the minimum torque, as specified in the applicable fastener standard, has been reached. The optimum recess torque values can be found in Table 3. f) Record the applied torque and mode of failure, if any. g) Disengage the fastener and driver. h) Repeat steps a) through g), applying torque in the removal direction, using the same driver bit and fastener. 6.6 Fastener recess torque values The torque values given in Table 3 represent the minimum torsional strength values of the driver bit according to ISO 4580. The torque values that the drive system in the fastener can transfer are dependent on the drive size, material and penetration depth. The deeper the recess, the higher the drive system strength. However, head and fastener geometry shall be considered to select the appropriate penetration depth. Refer to specific fastener standards for specific torque test values.