Full-Thread vs Standard A325 Hex Bolts: Benefits, Drawbacks, and Applications

🔹 Importance / Benefits of Full-Thread A325 Hex Bolts

Flexibility in Grip Length
- A full-thread bolt allows you to clamp parts of varying thicknesses without worrying whether the thread starts far enough down the shank.
- Useful when you don’t know the exact grip length during installation.
Adjustability
- Washers and nuts can be positioned anywhere along the bolt length, which helps in field conditions or temporary assemblies.
Inventory Reduction
- One full-thread size can serve for multiple grip ranges, reducing the number of different bolt lengths you need to stock.

Reduced Shear Capacity
- Threads cut into the shank reduce the effective shear area compared to an unthreaded shank.
- This is critical in structural applications (beam-to-column connections, splice plates, etc.) where shear forces dominate.
Stress Concentration
- Threads create stress risers. Under high tension or cyclic loading, fatigue performance is lower than with a smooth shank.
Not Code-Preferred for Structural Steel
- ASTM A325 bolts are normally partially threaded (thread length controlled by ASME B18.2.6).
- AISC and RCSC specifications require that the shear plane should ideally pass through the shank, not the threads. Using full-thread bolts in shear connections may fail inspection or require special approval.
Bending Resistance
- Smooth shanks resist bending better than threaded portions. In situations with eccentric loading, a full-thread bolt is weaker.

Full-thread A325 → good for clamping applications where tension load dominates, or where adjustability is needed, but usually requires engineer approval.
Standard (partially threaded) A325 → the default in construction, especially in structural steel joints where shear strength is critical.