SAE AS 7251C:2014 – Nuts, Self-Locking, Steel, Corrosion and Heat Resistant High Strength,All Metal 1200F Use, UNJ Thread Form.
3.9.3.1.2 Fixture
The spacer-type fixture shall be made of AMS5732 or AMS5737 steel. The diameter of the bolt hole in the fixture shall be 0.030 to 0.034 inch greater than the maximum major diameter of the bolt thread (see Figure 2). Fixture may be counter- bored 0.004 to 0.008 inch greater than the maximum allowable shank diameter of shank nuts to permit the spacer to seat onto the bearing surface of the nut. Alternative bolts lengths and elongations may be used provided they meet the requirements of 3.9.3.1.1
3.9.4 Permanent Set
At least three nuts shall be assembled on a maximum material bolt or stud (see Figure 3) so that the bolt or stud protrudes through the nut not less than three thread turns. Nuts shall then be removed from the maximum material bolt or stud and assembled on a minimum material bolt or stud (see Figure 4) In the same manner. Tests shall be conducted at room temperature with no axial stress; breakaway and prevailing torques shall be measured and recorded. The nuts shall not exceed the maximum prevailing torque of Table 3, Column 131, during the installation or removal cycle on the maximum material bolt or stud and shall not be less than the minimum breakaway torque of Table 3, Column Ill, at the start of the removal cycle on the minimum material bolt or stud.
3.9.5 Reusability
Nuts shall be assembled on test bolts conforming to 3.10 and tested in accordance with 3.9.3 as modified in 3.9.5.1,3.9.5.2, and 3.9.5.3. After testing, bolt threads to remain Serviceable and permit a new nut to assemble freely with the fingers, up to the self-locking device.
3.9.5.1 Twelve-Cycle, Room Temperature, As Received Test
Ten nuts shall be installed and removed from the bolts 12 consecutive times, using the same nut and bolt; breakaway and prevailing torques shall be measured and recorded. The nuts shall not exceed the maximum prevailing torque of Table 3, Column /3/, during the installation or removal cycle and shall not be less than the minimum breakaway torque of Table 3, Column /1/.
3.9.5.2 Five..Cycle. Loaded and Conditioned Test
Conditioning cycles shall be perfomied in accordance with 3.9.3.1. The nuts shall be completely removed from the bolt after each cyde of conditioning. The conditioning test shall be run five consecutive cydes, using the same nut, bolt and spacer; breakaway and prevailing torques shall be measured and recorded. The maximum prevailing torque and the minimum breakaway torque for each cycle shall not exceed the limits specified in Table 3. Columns 141 and /1/, respectively.
3.9.5.3 Single Cycle, Loaded. Room Temperature Test
Nuts shall be assembled and loaded to the assembly torque specified in Table 3, Column (5/. The nut shall be completely removed from the bolt; breakaway and prevailing torques shall be measured and recorded; and the nuts shall not exceed the maximum prevailing torque of Table 3, Column /3/, during the installation or removal cycle and shall not be less than the minimum breakaway torque of Table 3, Column (2/.
3.9.6 Vibration Test
Ten nuts of the type to be tested, for the sizes listed in Table 4, shall be installed on a test bolt conforming to 3.10 and on a test fixture as In 3.9.3.1.2. The assembly torque values shall be as specified In Table 4. For sizes not shown, the torque shall be as agreed upon by purchaser and vendor. Testing of nuts other than hexagon or double hexagon wrenching types shall be as agreed upon by purchaser and vendor. Five nuts shall be removed from the test bolts and reinstalled four additional times to the torque values specified for the thread size. The other five assembled nuts shall be baked at 1200 °F ± 15 °F for 6 hours ± 0.25 hours and cooled to room temperature; these nuts shall then be removed and reinstalled four additional times to the torque values specified for the thread size. The five baked nuts and five unbaked nuts shall be assembled on the vibration test fixture (see Figure 5) on test bolts and vibration tested at room temperature. Assemblies of nuts having Class 3B threads shall be vibrated 30000 cycles at a frequency of 1750 to 1800 cpm and an amplitude of 0.435 to 0.465 inch. The assembly shall traverse the entire length of the slots in the test fixture. Reference lines shall be scribed, or other suitable markings made, to determine the amount the nut turns on the test bolt during vibration test. The relative rotation between any nut and bolt shall be not greater than 360 degrees. The nuts shall not have developed any cracks or broken segments, as shown by examination at lox magnification. Multipiece floating plate nuts shall have the nut element removed from the retainer for this test. Fixed anchor nuts may have the lugs removed, Vibration testing is not required for nuts of nominal thread diameter less than 0.164 inch.