ISO Engineering


Shop For Carriage & Plow Bolts

Carriage Bolts, Plow Bolts & Timber Bolts

The common features of bolts in this selection are that they are drive-less featuring either a domed or flat head, and that they feature a square section underneath the head of the bolt which grips the application surface to prevent the bolt from turning. This type of bolt is commonly used with a nut and washer in timber and lumber applications, as well as on heavy machinery.

Carriage Bolt

A carriage bolt has a domed or countersunk head and the shank is topped by a short square section under the head of the bolt. The square section grips into the part being fixed, preventing the bolt from turning when the nut is tightened. Carriage bolts are often used to fasten wood panels or board to masonry or to one another. The square shank of the bolt allows it to lock into place when inserted into a round hole in wood or a square hole in a metal strap, the unthreaded square shank pulls into the wood creating a tight connection.

Carriage bolts are available in 18-8 Stainless Steel, Hot Dip Galvanized, and Zinc Plated 307 Grade A Steel. Each metal and finish offers its own benefits including hardened metal and corrosion resistance.

Plow Bolt

Plow bolts are designed with a short square countersunk section beneath the head of the bolt. This square section is used to prevent spinning while being fastened by a nut. Plow bolts are commonly used on plows and other heavy duty equipment. These bolts received their names from their use attaching the cutting edge of a plow to the plow blade. Plow bolts are stronger than standard bolts making them the ideal choice for heavy machinery.

Plow bolts are like carriage bolts but have a flat head that sits flush once installed. They have this flat head because they are commonly used where a domed head would be exposed. The flat head deters wearing and allows the bolt to last longer on the scouring surface (area where the head of the bolt would be exposed to high wear). Plow Bolts are measured from the top of the head all the way to the tip of the bolt. They can be removed by taking the nut off the bolt and tapping the tip with a hammer until the square section backs out of the hole.

Timber Bolt

A Timber bolt, also known as a Mushroom head bolt or Dome head bolt, is like a Carriage Bolt in appearance but with an oversized, heavy duty low profile head. Timber Bolts are typically used in marine and wood applications to protect timber structures from the elements. The underside of the oversize head of a timber bolt features rings that help prevent water from entering the hole and nubs or fins which prevent the bolt from turning. The timber bolt's oversize head eliminates the need for a washer on the bolt head side. Our Timber Bolts come in 3/4" and 5/8" size diameters.