STAINLESS STEEL HEXAGON HEAD BOLTS

Hexagon Head Bolts — Unlike a set screw, a Hexagon Head Bolt carries a plain, unthreaded shank beneath the head — a feature that only matters once you understand what it is for: locating precisely in a clearance hole and offering a full, unbroken cross-section across any shear plane in the joint. That makes it the preferred choice for through-bolted connections in structural steelwork, machinery frames, plant and process equipment, and general engineering assemblies where the fastener is paired with a nut rather than driven into a tapped hole. Anywhere a joint is loaded transversely as well as in tension, the plain shank resists shearing and wear better than a thread crest would. Grade selection follows the same logic as most stainless fixings: A2 handles the bulk of indoor, dry, and moderate-humidity work at a sensible cost, while A4 is worth the premium once the bolt is exposed to marine air, road salt, washdown chemicals, or sustained damp — its molybdenum addition holds off pitting corrosion that would otherwise progress steadily through an A2 bolt in the same environment. The standard behind this bolt, DIN 931 (now more commonly specified as its ISO 4014 equivalent), fixes the proportion of shank left unthreaded relative to the bolt's overall length, along with head dimensions and thread tolerance, so the plain section reliably lands where the joint needs it. Choosing the right one starts with the grip length: measure the total thickness being clamped, including any washers, and pick a bolt long enough that the plain shank spans the clearance holes while leaving enough thread proud to fully engage the nut. Diameter should match the calculated load and the size of hole already in the structure or fitting; where the joint is not shear-critical and a tapped hole is being used instead, a fully threaded set screw is usually the more practical and economical option.

FAQs
Does a hexagon head bolt need a washer?
A flat washer is common practice under the nut, and often under the head too, to spread bearing load and protect the surface finish from spanner marks; it is not mandatory for the bolt to function, but it is good practice on softer or coated materials.

How is bolt length chosen relative to grip length?
Length should be measured against the full clamped thickness, including washers, so the plain shank spans the joint and the nut has enough exposed thread to seat fully and develop the intended clamp load — an overly short bolt risks the nut running onto the transition between shank and thread.

Is ISO 4014 the same product as DIN 931?
They describe the same part-threaded hexagon bolt with closely aligned dimensions and tolerance classes; ISO 4014 is the actively maintained international standard and is increasingly the reference used on new drawings, though DIN 931 remains widely stocked and understood.

Can a hexagon head bolt be used in a tapped hole instead of with a nut?
It can, but the plain shank then serves no purpose and simply reduces the thread engagement available near the head; a fully threaded set screw is the more efficient choice for tapped-hole applications.