Round Head Bolts
What are round head bolts?
Round head bolts are heavy-duty fasteners with a smooth, domed head that presents no sharp edges and resists snagging. The head is driven or held from the nut side; anti-rotation features under the head (such as a square neck or nibs) prevent spinning during tightening. Common families include carriage bolts, plow bolts, and timber bolts.
Types of round head bolts we offer
- Carriage bolts — domed head with a square neck that bites into wood or steel to stop rotation. Ideal for decks, fencing, and general construction.
- Plow bolts — round or countersunk-style head with a square neck; designed for high-abrasion equipment and ground-engaging wear parts where a low-snag head is preferred.
- Timber bolts — large round head with anti-rotation lugs or nibs under the head to grip wood; used in heavy timber framing, bridges, and utility structures.
Materials & finishes for round head bolts
- Carbon / alloy steel — high strength for structural and machinery uses.
- Hot-dip galvanized steel — thick zinc coating for outdoor and marine-adjacent exposure.
- Zinc-plated steel — economical corrosion protection for general indoor or light outdoor use.
- Stainless steel (18-8 / 304) — broad corrosion resistance for most environments.
- Stainless steel (316) — enhanced resistance in coastal or chloride-rich locations.
Common applications for round head bolts
- Decks, docks, fences, playgrounds, and site furnishings
- Heavy equipment, agriculture implements, and wear parts (plow bolts)
- Timber framing, bridges, pole-barns, and utility structures (timber bolts)
- Railings, guardrails, and assemblies where snag-free heads are preferred
Why choose round head bolts
- Smooth, safe profile — domed head reduces snagging and protects finished surfaces.
- Anti-rotation under-head features — square necks or nibs speed installation from one side.
- Versatile materials — galvanized and stainless options for demanding weather exposure.
- Wide size range — inch and metric diameters with ample length selections.
How to size and specify round head bolts
Order by diameter × length (measured from under the head to the end of the bolt) and the required thread (coarse/fine or metric). Select a neck style (square neck or nibbed) that matches your substrate, and pair with compatible nuts, flat washers, and lock washers as needed.
Installation tips for round head bolts
- Seat the square neck or nibs fully by pulling the joint snug before final torque to prevent head spin.
- Use flat washers to protect wood fibers or painted surfaces; add lock washers or threadlock where vibration is present.
- For exterior builds, match bolt and hardware materials (e.g., hot-dip galvanized with galvanized nuts/washers) to avoid galvanic issues.
Round Head Bolts FAQs
See the accordion below for quick answers about carriage vs plow vs timber bolts, sizing, materials, and best practices.
Carriage bolts have a domed head with a square neck for general construction; plow bolts use a low-snag round or countersunk-style head for equipment wear parts; timber bolts add under-head lugs/nibs for extra bite in heavy timbers.
From under the head to the end of the bolt. (Countersunk styles are measured overall.)
Hot-dip galvanized for robust weather protection; 304 stainless for broad corrosion resistance; 316 stainless for coastal/chloride exposure.
Flat washers distribute load and protect surfaces; lock washers or thread-locking methods help resist loosening in vibration.
The neck is designed to bite and prevent rotation. Use a washer or consider a nibbed timber bolt when surface marring must be minimized.
Match thread and material/finish (e.g., galvanized nuts for galvanized bolts, stainless nuts for stainless bolts) to maintain corrosion compatibility.