MS51959 : Mil-Spec Hardware
MS51959 : 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 (not available 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. UNDERCUT HEAD: Screws above the dashed line in Table I shall have undercut heads.
7. RECESS: Recess shall be in accordance with MS9006.
8. MATERIAL IDENTIFICATION MARKING: Type 316 (UNS S31600) or Type 316L (UNS S31603) CRES
screws nominal size.1900 and larger shall be permanently marked “316”. Markings shall be raised or depressed on
the screw head at manufacturer’s option.
9. 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.
10. FINISH CODE:
Passivate - No code letter after dash number, or after material code (if applicable) indicates passivate.
Black Oxide - “B” after dash number (not available for Type 316 or Type 316L CRES), indicates black
11. 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).
MS51959-1 indicates Screw, Machine-Flat Countersunk Head, 82°, Cross-Recessed, 300
Series CRES, Passivated; .0860-56 UNC-2A Nominal Thread Size, .125
MS51959-1B indicates Screw, Machine-Flat Countersunk Head, 82°, Cross-Recessed,
Optional 300 Series CRES, Black Oxide Coated; .0860-56 UNC-2A Nominal
Thread Size, .125 Length
MS51959-1S316 indicates Screw, Machine-Flat Countersunk Head, 82°, Cross-Recessed,
Type 316 CRES; Passivated; .0860-56 UNC-2A Nominal Thread Size, .125
- 1. All dimensions are in inches.
- 2. Interpret drawing in accordance with ASME Y14.5M.
- 3. In the event of a conflict between the text of this document and the references cited herein, the text of this document
- shall take precedence.
- 4. Unless otherwise specified, issues of referenced documents are those in effect at the time of solicitation.
- 5. MS51959 Flat Countersunk Machine Screws manufactured prior to 25 April 1997 may be used until stock is depleted.
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