Imperial Hex Head Bolt – Brief Introduction

1. Standards & Specifications
Standards: Compliant with **BS 916** (British Standard) or ANSI/ASME B18.2.1** (US imperial), inch-based sizing.
Thread: **BSW** (Whitworth, coarse) or **BSF** (British Standard Fine) threads (e.g., 1/2″-12 BSW).
Marking: Grade denoted by radial lines (e.g., 3 lines = Grade 8) or numeric codes.

2. Material & Grades
Materials:
Carbon Steel: Grades 4.6, 8.8, or 10.9 (common for general to high-strength use).
Stainless Steel: 304 (A2), 316 (A4) for corrosion resistance.
Alloy Steel: Heat-treated for extreme loads.
Surface Treatment: Zinc-plated, hot-dip galvanized, or phosphate-coated.

3. Key Features
Hex Head Design: Compatible with imperial wrenches (e.g., 1/2″ bolt uses 3/4″ wrench).
Thread Profile: 55° Whitworth thread angle (vs. 60° metric/UTS), reducing stress concentration.
Length Measurement: From under-head to tip (e.g., 1/2″×3″ = ½” diameter, 3″ length).

4. Applications
Legacy Machinery: Maintenance of vintage British equipment.
Marine & Rail: Ships, locomotives using imperial systems.
Construction: Structural connections in regions adhering to imperial standards.

5. Comparison with Metric Bolts
Units: Inches (imperial) vs. millimeters (metric).
Thread Standards: BSW/BSF (imperial) vs. ISO metric (M-series).
Wrench Sizes: Imperial wrenches (e.g., SAE) vs. metric tools.

6. Notes
Avoid mixing with metric bolts to prevent thread damage.
Use thread lubricant in high-torque applications.
Select stainless steel or coatings or humid/salty environments.

Summary: Imperial hex bolts, with Whitworth threads and inch-based sizing, remain essential for legacy systems, offering robust fastening in mechanical, marine, and industrial applications.