Skip to main content Skip to search Skip to main navigation

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.