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MS21059 : Mil-Spec Hardware

MS21059 : Mil-Spec Hardware Specification
Nut, Self-Locking, Plate, Two-Lug, Floating, Low Height, Steel, 125 KSI, Ftu, 450°F

MS21059 CAD DrawingClick on drawing for larger view


1. MATERIAL: Nut - carbon steel, compositions 1035 (UNS G10350) 1040 (UNS G10400) and 1050 (UNS G10500) in accordance with ASTM A827 or QQ-S-700 1042 (UNS G10420) in accordance with ASTM A29 alloy steel grades 4130 (UNS G41300) 4340 (UNS G43400) and 8740 (UNS G87400) in accordance with ASTM A29 Retainer (if applicable) – carbon steel compositions 1035 (UNS G10350) and 1050 (UNS G10500), in accordance with ASTM A827 or QQ-S-700 1074 (UNS G10420) and alloy steel grade 4130 (UNS G41300) in accordance with ASTM A29

2. FINISH: Cadmium plate in accordance with QQ-P-416 Type II, Class 2. For dry film lubricated nuts the type and class are optional if the nuts meet the salt spray requirements of QQ-P-416 Type II

3. DIMENSIONING AND TOLERANCING: Dimensioning and tolerancing shall be in accordance with ANSI Y14 5M


5. THREADS: Threads before lubrication in accordance with MIL-S-8879

6. SURFACE TEXTURE: Surface texture unless otherwise specified shall not exceed 125 microinches, in accordance with ANSI/ASME B46 1

7. LUBRICANT: Dry film lubricant approved in accordance with MIL-N-25027 Non-dry lubricants shall be soluble in the cleaner specified in MIL-5-8802

8. COUNTERBORE/COUNTERSINK: On size .164 and larger thread relief shall be .062 minimum, on size .138 and smaller, countersink or radiused within “P” diameter

9. FLOAT: Float of nut element portion of assembly shall not be less than .030 laterally and longitudinally from centered position nut body shall be capable of engagement with a bolt in the maximum misaligned position maximum axial float .020 inches for .190 and smaller, .030 for .250 and larger nut misalignment shall not exceed dimension “B” the nut and base portion of the assembly shall form one integral unit and the surface assembly shall provide a bearing for the nut

10. PART NUMBER: The part number shall consist of the basic MS number followed by a dash number from Table 1

Example MS21059L4K

  • MS21059 Basic MS Number
  • L4K Dash Number

MS21059L4K indicates nut self-locking, plate, two lug, floating low height steel 125 KSI Ftu 450?F 250-28 UNJF-38, dry film lubricant countersunk or dimpled holes


  • 1. All dimensions are in inches
  • 2. In the event of a conflict between the text of this standard and the references cited herein the text of this standard shall take precedence
  • 3. Referenced government (or non-government) documents of the issue listed in that issue of the Department of Defense Index of Specifications and Standards (DODISS) specified in the solicitation form a part of this standard to the extend specified herein
  • 4. Design and usage limitations these nuts are designed to develop the tensile strength of bolts and screws with an ultimate tensile strength of 125 KSI based on the cross section area at the basic root diameter of the threads. These nuts are designed to be used on 3A external threads. These nuts shall be used in accordance with the limitations of MS33588. Only nuts which there are qualified products listed on QPL 25027 shall be used.
  • 5. MS21059 supersedes NAS686 NAS1031

Interchangeability Relationship

MS21059 nuts can universally replace NAS686 and NAS1031 nuts of like material, thread size lubricant (dry film or non-dry film) rivet spacing and fastening method (plain rivet holes dimpled or countersunk rivet holes) but these NAS686 and NAS1031 nuts cannot universally replace MS21059 nuts.

Need the Spec?

Click here to download MS21059 Specification
(PDF Format).

Great Lakes Fasteners
2204 East Enterprise Parkway
Twinsburg, Ohio 44087

Ohio: 330-425-4488
Nationwide: 800-589-4578
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GLFTechnical Fastener Supply specializes in a wide range of industrial and military specification (MIL Spec) fasteners; including MS fasteners, AN Fasteners, and NAS Fasteners.