Video: Making of a Square Head Machine Bolt

Take a quick tour of our shop and follow an order of 7/8″ diameter square head machine bolts through the manufacturing process. This video includes shearing, pointing, hot forging, roll threading, and galvanizing. Find out what it takes to make an order of large, custom machine bolts. See more videos on our channel at


Hello, my name is Anthony Porreco and I am an estimator here at Portland Bolt & Manufacturing Co.

What you are looking at is a 7/8 x 26 inch long square head machine bolt, which is a common style of pole-line fastener made here at our facility in Portland, Oregon.

As you can see, this machine bolt has a standard thread length of 6 inches, an added semi-cone point, and is hot-dip galvanized.

Square head machine bolts that we manufacture for the pole-line industry are used to fasten wooden crossarms to telephone poles.

For this particular job, approximately 500 of these machine bolts were made.

Portland Bolt manufactures square head machine bolts for pole-line applications throughout the country, and we perform all of the manufacturing processes right here at our 85,000 square foot facility.

Now we’ll take you through a step-by-step look at the various processes involved in manufacturing and galvanizing a square head machine bolt.

The square head machine bolts for this order are manufactured from A36 mild steel round bar which we receive in 20-foot lengths from a steel mill in McMinnville, Oregon.

After the steel is removed from the racks, the first step in the manufacturing process is cutting the bars of steel to length.

This is done on one of our shears, which chops the steel like a guillotine. This method of cutting is fast and efficient.

Once the material is cut to length, we’ll put a semi-cone point on the end prior to threading.

The purpose of the semi-cone point is to provide ease of installation into the wooden member, without the threaded end of the bolt getting snagged on the wood.

The semi-cone point is added to, not included in, the length of the bolt.

Once the cut-to-length round bar is pointed, they move on to threading.

There are two methods used to thread bolts: roll-threading and cut-threading.

Roll-threading is an extrusion process in which pitch diameter steel round bar is forced between two dies to form the threaded portion of the bolt instead of being removed as in cut-threading.

Because of the size and quantity of pole-line fasteners typically required at a time, roll-threading is the preferred method due to the efficient nature of the process.

The next step in manufacturing a square head machine bolt 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 square head is then forged onto the heated end of the bar, including the grade symbol and manufacturer’s marking, which is stamped directly onto the head of the bolt.

Now that the bolts are 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 prepped so that the steel bonds properly with the zinc.

The pickling process involves submerging the bolts in caustic soda, rinsing, and then submerging them in sulfuric acid.

This process removes 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 zinc has been properly spun out of the threads.

After the bolts have been inspected, a square nut is assembled to each bolt.

This is a common procedure with pole-line fasteners as a means of keeping all associated parts together.

Finally, the bolts are put in boxes, palletized, and marked clearly with the destination and contents, and any other information required.

The order is then put on a truck on the day we promised to ship, and sent to its final destination.

For more information about square head machine bolts, other pole-line hardware, or Portland Bolt in general, call, or visit us at

You can also find more information pertaining specifically to pole-line fasteners at