Views: 0 Author: Site Editor Publish Time: 2026-05-08 Origin: Site
Threads are the core functional part of a screw. Without threads, a screw cannot generate clamping force. Different thread types suit different materials, loads, and applications. Understanding basic thread parameters (profile, pitch, diameter, direction) is critical for correct selection.
Taiyuanfeng provides a full set of thread inspection tools (thread gauges, ring gauges, plug gauges) to ensure every screw thread is qualified.
1. Basic Thread Parameters
Major diameter | Largest diameter of thread (nominal diameter) |
Pitch diameter | Critical diameter that determines fit accuracy |
Minor diameter | Smallest diameter of thread (root diameter) |
Pitch | Distance between adjacent thread crests (metric) |
Threads per inch (TPI) | Number of threads per inch (imperial/Unified) |
Thread angle | Angle between thread flanks (metric 60°, BSW 55°) |
Hand of thread | Right-hand (common) or left-hand |
Taiyuanfeng offers custom threads, including left-hand threads and multi-start threads.
2.1 Metric Thread (M)
Features：60° thread angle, denoted as “M + major diameter × pitch” (pitch omitted for coarse). Most universal worldwide.
Applications：Machinery, automotive, electronics, appliances (global market).
Taiyuanfeng Advantage：We offer metric threads from M2 to M12, tolerance classes 4h to 6g.
2.2 British Standard Thread (BSW / BSF)
Features：55° thread angle, denoted as “diameter (inch) – TPI”. BSW coarse, BSF fine.
Applications：Old British/Commonwealth equipment, pipes, repair parts.
Taiyuanfeng Advantage：Regular stock of BSW/BSF threads, fast delivery available.
2.3 Unified Thread (UNC / UNF)
Features：60° thread angle, not interchangeable with metric. UNC coarse, UNF fine, UNEF extra fine.
Applications：US & North American machinery, aerospace, hydraulic components.
Taiyuanfeng Advantage：We supply UNC/UNF screws, supporting 2A/2B fit classes.
2.4 Self-Tapping Thread
Features：Special thread profiles (e.g., tri-lobular, alternating heights), for plastic or sheet metal – no pre-tapping.
Applications：Plastic enclosures, sheet metal, electronics assembly, furniture.
Taiyuanfeng Advantage：We offer multiple self-tapping designs (ST, PT, Taptite, etc.) to reduce assembly cost.
2.5 Pipe Thread (NPT / BSPT / BSPP)
Features：Tapered or parallel thread, seals via thread interference or gasket. Used for pipes.
Applications：Water pipes, air lines, hydraulic lines, valves.
Taiyuanfeng Advantage：We offer NPT, BSPT, BSPP threaded screws and fittings with reliable sealing.
3. Thread Fit & Tolerance
Metric tolerance classes: External threads (4h, 6g, 6h, etc.), internal threads (5H, 6H, etc.)
Unified fit classes: 1A/1B (loose), 2A/2B (medium), 3A/3B (tight)
Selection principle: Use 6g/6H for general applications; use 6h or looser fit for high-strength or thick coatings
Taiyuanfeng recommends the best thread fit class based on your assembly needs and surface finish, with inspection reports.
Requirement | Recommended Thread |
Worldwide universal | Metric (M) |
US market | UNC / UNF |
Old British equipment | BSW / BSF |
Plastic / sheet metal | Self-tapping |
Pipe sealing | NPT / BSPT |
Fine adjustment or thin wall | Fine thread (UNF, M fine) |
Issue | Cause | Solution – Taiyuanfeng |
Stripping | Fit too loose or material too soft | Select correct fit class or use thread inserts |
Galling | Stainless steel friction heats and welds | Apply anti-seize coating or use plated screws |
Breakage | Stress concentration at thread root | Use thread rolling instead of cutting, add radius |
Hard to start | Pitch or thread angle deviation | Inspect with go/no-go gauge, control coating thickness |
Taiyuanfeng uses precision thread rolling and automatic optical thread inspection to ensure consistency and go/no-go rate.
Threads are the technical core of screws. Correctly selecting thread type, pitch, and fit class significantly improves assembly efficiency, locking performance, and lifespan. Metric
Contact Taiyuanfeng for thread selection guidance and free samples.
