MS51957 : Mil-Spec Hardware
MS51957 : Mil-Spec Hardware Specification
Screw, Machine, Pan Head, Cross-Recessed, Corrosion Resistant Steel, UNC-2A
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1. MATERIAL: Austenitic Corrosion-Resistant Steel screws shall be manufactured from Type 302 (UNS
S30200), Type 304 (UNS S30400), Type 304L (UNS S30403), Type 305 (UNS S30500), Type 316 (UNS
S31600), Type 316L (UNS S31603), Type 384 (UNS S38400), or Type XM-7 (UNS S30430) in accordance with
chemical composition specified in QQ-S-763. (See Material Identification Marking and Material Code).
2. FINISH: Passivate in accordance with QQ-P-35 or Black Oxide coating (except for Type 316 or Type 316L)
in accordance with MIL-C-13924, Class 4. (See Finish Code).
3. MECHANICAL PROPERTIES: The minimum tensile strength in load pounds, indicated for each size in Table I, is based on 80,000 PSI Minimum Tensile Strength. Load pounds are calculated by the stress areas indicated in FED-STD-H28/2. The yield strength, based on .2 percent offset, shall be 30,000 psi minimum.
4. MAGNETIC PERMEABILITY: When specified, screws shall have a magnetic permeability of less than 2.0
maximum (air = 1.0) for a field strength H=200 Oersteds using a magnetic permeability indicator per ASTM A 342.
Note: Cold working screws may not be capable of meeting permeability and strength requirements simultaneously.
5. THREADS: Screw threads shall be Unified external threads Class 2A UNC in accordance with FED-STDH28/
2. Acceptability of screw threads shall be in accordance with FED-STD-H28/20. Threads shall extend to
within two threads or less of the bearing surface of the head, except that all lengths over 2.000 inches shall have a
minimum complete thread length of 1.750 inches.
6. RECESS: Recess shall be in accordance with MS9006.
7. MATERIAL IDENTIFICATION MARKING: Type 316 (UNS S31600) or Type 316L (UNS S31603) CRES
screws nominal size #10 (.1900) and larger shall be permanently marked “316”. Markings shall be raised or
depressed on the screw head at manufacturer’s option.
8. MATERIAL CODE:
For 300 Series CRES - No code after dash number indicates any 300 Series Austenitic
Corrosion-Resistant Steel listed in material requirement
For Type 316 or Type 316L CRES - “S316” after dash number indicates Austenitic Corrosion-
Resistant Steel Type 316 or Type 316L.
9. FINISH CODE:
Passivate - No code letter after dash number, or after material code (if applicable) indicates
Black Oxide - “B” after dash number, (not available for Type 316 or Type 316L CRES),
indicates black oxide coating.
10. PART NUMBER: The part number shall consist of the basic MS number, followed by a dash number from
Table I, a material code (if applicable), and a finish code (if applicable).
MS51957-1 indicates Screw, Machine-Pan Head, Cross-Recessed, Optional 300 Series
CRES, Passivated; .0860-56 UNC-2A Nominal Thread Size, .125 Length
MS51957-1B indicates Screw, Machine-Pan Head, Cross-Recessed, Optional 300 Series
CRES, Black Oxide Coated; .0860-56 UNC-2A Nominal Thread Size, .125
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