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National Aerospace Standard

NAS6603 — Close-Tolerance Hex Head Bolt

NAS6603 (part of the NAS6603–NAS6620 family) covers close-tolerance, hex-head tension bolts machined from alloy steel with a reduced major diameter and long thread, rated to 160 KSI Ftu. It's used where a precision shank fit is required in structural aerospace joints.

Type: Hex Head Bolt, Close Tolerance Tensile: 160 KSI Ftu Thread Class: 3A Issuing Body: AIA Status: Active

At a Glance

Full Title
Bolt, Tension, Hex Head, Close Tolerance
Thread
UNJF-3A, Right-Hand, Long Thread
Base Material
Alloy Steel (MIL-S-5000 / AMS 6322)
Surface Treatment
Cadmium Plate, QQ-P-416 Type 2 Class 2
Locking Options
Self-Locking or Nonlocking
Head Style
Hex Head, Reduced Major Diameter
Related Series
NAS1103 / NAS1303 (same grip table)
Issuing Body
Aerospace Industries Association

Overview

NAS6603 is one entry in the NAS6603-through-NAS6620 family of close-tolerance, hex-head tension bolts. These are precision-shank alloy steel bolts with a reduced major diameter and long thread, rated to a minimum tensile strength (Ftu) of 160 KSI, and are produced in both self-locking and nonlocking configurations.

Material is qualified to MIL-S-5000 or MIL-S-6049 (or the AMS 6322 second material response), with a cadmium plate finish per QQ-P-416 Type 2, Class 2. Threads are UNJF Class 3A, right-hand, and grip lengths in the series track the same dash-number grip table used by the related NAS1103 close-tolerance bolt series — NAS1303 uses the same body but with a longer thread length per dash number.

  • Add "C" before the dash number to specify a corrosion-resistant-steel version of the bolt.
  • Add "DD" before the dash number for an aluminum alloy bolt.
  • Add "A" after the dash number for an undrilled shank, or "H" before the dash number for a drilled head and shank.

Part Number Reference

Dash number sets grip and length; letter codes before/after the dash modify material and drilling.

NAS6603-4
NAS6603-4 decodes to: Alloy steel close-tolerance hex head bolt, cadmium plated, drilled shank, grip .250".

Material & Process Callouts

RequirementGoverning Document
Base Material (Alloy Steel)MIL-S-5000 or MIL-S-6049 / AMS 6322
Surface TreatmentQQ-P-416, Type 2, Class 2 (Cadmium Plate)
Thread FitUNJF Class 3A, Right-Hand
Tensile Strength160 KSI Ftu minimum
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NAS6603 shares grip values per dash number with the NAS1103 close-tolerance bolt series; NAS1303 uses the same body with a longer thread length per dash number. Confirm drilled/undrilled and material variant call-outs against the applicable engineering drawing before substituting between series.

NAS6603 — Frequently Asked Questions

What does "close tolerance" mean for NAS6603?

The bolt shank is held to a tighter diametral tolerance than a standard structural bolt, giving a precision interference or close-clearance fit in the drilled hole — important for shear-critical structural joints.

What's the difference between self-locking and nonlocking NAS6603 bolts?

Both configurations are covered under the same NAS6603 drawing; the self-locking version incorporates a thread-locking feature, while the nonlocking version relies on a separate locking device such as a self-locking nut or cotter pin.

How does NAS6603 relate to NAS1103 and NAS1303?

NAS6603 and NAS1103 share the same grip-to-dash-number table. NAS1303 uses the same body but has a longer thread length for each dash number, making it suited to thicker grip stacks needing more thread engagement.

Need NAS6603 Bolts to Print?

Ananka Fasteners manufactures NAS6603 close-tolerance bolts with full material traceability and Mill Test Certification on every lot.

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