SAE AS 7251C:2014 pdf free download – Nuts, Self-Locking, Steel, Corrosion and Heat Resistant High Strength,All Metal 1200 F Use, UNJ Thread Form

SAE AS 7251C:2014 pdf free download – Nuts, Self-Locking, Steel, Corrosion and Heat Resistant High Strength,All Metal 1200 F Use, UNJ Thread Form.
3.4.1 Bearing Surface Squareness
The bearing surface shall be square (flat to concave) with the thread pitch cylinder axis within the limits specified on the part drawing. Bearing surface shall not be convex. Bearing surface squareness shall be tested using a table squareness gage and feeler gage, The squareness requirement shall apply to the complete beanng surface of the nut except that, for nonfloating plate nuts having a bearing surface exceeding 1.5 times (tie thread major diameter, the squareness requirement shall, unless otherwise specified on the part drawing, apply only to the portion of the bearing surface of the nut contained within a diameter equal to 1.5 times the thread major diameter. The nuts to be inspected shall permit at least three complete turns of engagement on the thread arbor of the squareness gage; plating or coating may be stripped, if necessary, to meet this requirement. Multip.eoe floating plate nuts shall have the nut element removed from the retainer for checking thread squareness.
3.4.2 Plating
Internal thread plating or coating allowance shall be as specif led in AS8879, unless otherwise specified on the part drawing.
3.5 Heat Treatment
The nuts shall be precipitation heat treated after forming to meet the performance requirements specified.
3.51 Hardness
Unless otherwise specified on the part drawing. the core hardness after heat treatment as in 3.5 shall be no greater than 46 HRC (see 8.1). determined in accordance with MIL-STD-1312-6 (in accordance with NASM 1312-6). The minimum limit is controlled by the axial tensile strength requirement in 3.9.1.
3.6 Fluorescent Penetrant Inspection
Prior to any required plating or coating and following all forming, deformation and heal treatment, parts shall be subject to fluorescent penetrant inspection in accordance with ASTM E14171E1417M, Type I. Sensitivity Level 2 minimum. Acceptance cnteria of surface discontinuities shall be in accordance with AS3071.
3.7 Plating
Nuts shall be silver plated in accordance with AMS241 1 • unless otherwise specified on the part drawing. On nuts with
thread sizes 0.250 inch and larger, the plating thickness shall be not less than 0.0002 inch when measured on the thread
pitch diameter, Microscope measurement on a sectioned nut shall be used as a referee method. Nuts with thread sizes
0.190 inch and smaller shall show complete plate coverage on the thread. Plating on other surfaces shall be 0.0003 to
0.0006 inch thick.
3.8 Lubrication
The nuts may be provided with a wax type coating (such as cetyl alcohol) which will prevent nut-bolt seizure at initial installation provided such treatment is applicable to all production nuts of the same part number.
3.9 Performance
Unless otherwise specified on the part drawing, nuts shall conform to the applicable requirements of Section 3. All tests shall be conducted on representative nuts assembled on bolts of any convenient length and on which the nuts will assemble freely. with the fingers, up to the self-locking device.
3.9.2 Wrench Torque
This test is applicable to wrenching nuts with hexagon or double hexagon wrenching feature. For this test only, all nuts shall be cleaned to remove all traces of any supplemental lubricant (Such as wax. cetyl alcohol, etc.). At least three nuts shall be tested at room temperature for wrench torque by assembling a nut on an alloy steel bolt having sufficient strength. The nut shall be fightened against a bushing with a hole diameter as in 3.9.1 and having hardness not lower than 40 HRC, and surface roughness of 63 microinches Ra. Nuts shall withstand 12 successive applications of the torque specified in Table 2 without destroying the wrenchability of the nut, Wrenches used for this test can be open ended type or socket type.
3.9.3 Locking Feature Torque
The locking feature torque-shall be measured and recorded for not less than 10 new nuts, selected at random from the lot, for each of the tests required in 3.9.5. Loading and conditioning for the five-cycle test of 3.9.5.2. shall be in accordance with 3.9.3.1. Test bolts shall conform to 3.10 or equivalent threaded parts. Test fixtures shall conform to 3.9.3.1 .2. Tests shall be conducted at room temperature. The end of the bolt shall extend a minimum of 1.5 thread turns through the top of the nut at the start of the test. Test shall be run in such a manner that a dependable measure of torque will be obtained. The increase in temperature of the nuts during the test shall not exceed 74 DF. The maximum prevailing and minimum breakaway torque (see AS 1310) shall not exceed the values specified in Table 3 as required by the reusability tests in 3.9.5.