Video: Making of a Timber Bolt

Watch and learn as we follow an order of timber bolts through the shop at Portland Bolt. See shearing, hot-forging, roll threading, and hot-dip galvanizing of these 3/4″ x 24″ timber bolts. See more videos on our channel at


Hello, my name is Mike Monlux with Portland Bolt & Manufacturing Co.

I’m holding in my hand a 3/4″ x 24″ galvanized timber bolt. These are also referred to as economy bolts, dome-head bolts, or mushroom head bolts. The oversized, dome-shaped head on these bolts creates a large bearing surface eliminating the need for a malleable iron washer under the head. These bolts are commonly used in marine construction and the final destination for this particular bolt is Hydaburg, Alaska.

For this order, we made over 6,000 timber bolts in various lengths, in both 3/4″ and 5/8″ diameter. Portland Bolt manufactures timber bolts for marine projects throughout the country, and even overseas. And we perform all of the manufacturing processes, including hot-dip galvanizing, right here in our facility in Portland, Oregon. Right now we’ll take you through a step-by-step look at the various manufacturing processes involved in making these bolts.

The timber bolts for this order are manufactured from A36 mild steel material, which we receive in 20-foot lengths from a steel mill just down the road in McMinnville, Oregon. After the steel is taken off the racks, the first step in the manufacturing process is cutting the bars of steel to length. This is done by shearing the steel, a process which cuts the steel extremely efficiently, chopping the steel like a guillotine.

The next step in making timber bolts, is to hot-forge the head of the bolt. An induction heating coil heats the end of the round bar to approximately 2,000 degrees Fahrenheit. The timber bolt head is then forged onto the heated end of the bar. After the bolts are headed, they move on to threading.

There are two distinctly different ways that bolts can be threaded: cut threading and roll threading. These bolts will be roll threaded. Roll threading is an extrusion process in which steel round bar is forced between two dies to form the threaded portion of the bolt, instead of being removed as in cut threading. Roll threading is another very efficient operation, which results in a cost savings for the customer.

Now that the bolts have been made, the final step is to galvanize them in our hot-dip galvanizing tank. Before the bolts are dipped in zinc, however, they must be prepared so that the steel bonds properly with the zinc.

The pickling process involves submerging the bolts in caustic soda, rinsing them, and submerging them in sulfuric acid. These processes remove any scale and prepares the surface of the steel to accept the zinc. The bolts are then placed in our hot-dip galvanizing tank, which is filled with 840 degree molten zinc.

After the bolts are removed from the zinc, they are spun in a high-speed, centrifuge system to spin any excess zinc from the threads, so that they easily accept a nut. The bolts are then cooled in quench tanks, and inspected to ensure that the excess zinc has been properly spun out of the threads.

The bolts are then put in boxes, palletized, and marked clearly with the destination, contents, and any other relevant information. The order is then put on a truck, on the day we’ve promised to ship, and sent on its way, to its final destination.

For more information on timber bolts, or Portland Bolt in general, please visit