SAE AS 7251C:2014 pdf free download – Nuts, Self-Locking, Steel, Corrosion and Heat Resistant High Strength, All Metal 1 200 °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 bearing surface of the nut except that, for nonfloating plate nuts having a bearing surface exceeding 1 .5 times the 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. Multipiece floating plate nuts shall have the nut element removed from the retainer for checking thread squareness.
3.5.1 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-1 31 2-6 (in accordance with NASM 1 31 2-6). 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 heat treatment, parts shall be subject to fluorescent penetrant inspection in accordance with ASTM E1 41 7/E1 41 7M, Type I, Sensitivity Level 2 minimum. Acceptance criteria 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. Microscopic measurement on a sectioned nut shall be used as a referee method. Nuts with thread sizes 0.1 90 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.