1. Standards & Specifications
Standards: Compliant with **ASTM** (e.g., ASTM A307, A325) or **SAE J429**, using **imperial units (inches)**.
Thread: **Unified Thread Standard (UTS)** – **UNC** (coarse) or **UNF** (fine), e.g., 1/2″-13 (½” diameter, 13 threads per inch).
Markings Grade identification (e.g., Grade 2, 5, 8) via radial lines or raised numerals.

2. Material & Grades
Materials:
Carbon Steel: Grade 2 (low strength), Grade 5 (medium), Grade 8 (high strength, ~150 ksi tensile).
Stainless Steel: 304 (A2), 316 (A4) for corrosion resistance.
Alloy Steel: Heat-treated for extreme loads (e.g., ASTM A490).
Coatings: Zinc-plated, hot-dip galvanized, or phosphate-coated for rust prevention.

3. Key Features
Hex Head Design: Compatible with SAE wrenches/sockets (e.g., ¾” wrench for ½” bolt).
Thread Options: Full or partial threads (e.g., ASTM A325 for structural joints).
Strength: Grade 8 bolts offer high tensile strength (~150 ksi) for heavy-duty applications.

4. Applications
Automotive: Engine blocks, suspension systems, and chassis assembly.
Construction: Steel bridges, pipelines, and building frameworks.
Heavy Machinery: Mining, agriculture, and industrial equipment.
Aerospace: High-strength fastening in compliance with NAS/MS standards.

5. Comparison with Metric Bolts
Units: Inches (imperial) vs. millimeters (metric).
Thread Standards: UNC/UNF (UTS, 60° angle) vs. ISO metric (M-series, 60° angle).
Grade vs. Class: US Grade (e.g., Grade 8) vs. metric class (e.g., 10.9).

6. Notes
Material Pairing: Match nut grade to bolt grade (e.g., Grade 8 nut for Grade 8 bolt).
Corrosion Protection: Use stainless steel (A4) or coatings in marine/humid environments.
Torque Limits: Follow ASTM torque specifications to avoid over-tightening.

Summary: US-standard hex bolts, with imperial sizing and UTS threads, deliver robust performance in high-stress industries like automotive, construction, and aerospace, prioritizing durability and interchangeability.