The carriage bolt is a threaded fastener that is typically employed in wood applications, although some specialized versions can also be utilized to fasten metal components. Also dubbed coach bolts or plow bolts, the fastener has a design similar to a standard bolt. The main difference between the regular version and carriage bolts consists of […]

The carriage bolt is a threaded fastener that is typically employed in wood applications, although some specialized versions can also be utilized to fasten metal components. Also dubbed coach bolts or plow bolts, the fastener has a design similar to a standard bolt. The main difference between the regular version and carriage bolts consists of the domed head that is twice the diameter of regular bolt shafts.

carriage bolts for metal applications
The specific design of the carriage bolts
A further noteworthy difference between the carriage bolts and its traditional counterpart is the fastening mechanism. The design of the carriage bolt's head makes the use of a screwdriver or other drilling devices impossible. This is why carriage bolts come with a square fitting or shank protruding from its flat side. In addition to fastening, the shank also helps grip the material, preventing it from twisting or turning, therefore making the installation or assembly simple and straightforward.
The carriage bolt variation designed for metal applications include a ribbing under the rounded head instead of the square fitting. Similar to the fasteners designed for woodworking applications, the variation helps keep the metal components in place for a better fastening. Both types of carriage bolts are commonly utilized with nuts to help secure the materials in place.

 
Pre-installation requirements of carriage bolts
Irrespective of whether you intend to use them for a wood or a metal application, you will need to prepare a pre-drilled hole first. The reason for this comes from the specific shape of the head – rounded and smooth – that doesn't allow you to employ a drilling device. It is necessary to mention that the rounded mushroom-like shape of the head is what makes carriage bolts ideal for wood applications. In fact, the head's size and form prevents the bolt from being pulled into the wood, regardless of whether you used a washer or not.
Carriage bolt wood applications
Carriage bolts are safe and reliable fasteners you can use in any application that entails securing two planks together. Commonly seen in home construction, pilings, ready-to-assemble furniture, fences, patios and outdoor decks, carriage bolts are also a primary choice due to their aesthetic appeal. They are typically the number one choice for applications where smoothness is desired, as they can add a 'finished' look to any surface.
Carriage bolt metal applications
As previously mentioned, due to the unique advantages it comes with, the carriage bolt is ideal for wood applications. However, the truth is that you can employ a carriage bolt anywhere you would use a regular bolt. To ensure a snug fit between two metal components, you need to make sure that the hole in which the fastener goes has an identical size with the square shank.
Without denying that the process is more tedious, you can use a carriage bolt fastener in a metal application. As long as you remove the drill to test it and check the progress regularly, you can be sure it will hold firmly. Moreover, for metal applications it is advisable to add a washer and nut on the other side for improved fastening.

About the Author

Larry Melone
By Larry Melone
President

Started my career in the fastener world in 1969 at, Parker Kalon Corp. a NJ based screw manufacturer located in Clifton, NJ working in inventory control, scheduling secondary production and concluding there in purchasing. In 1971 I accepted a sales position at Star Stainless Screw Co., Totowa, NJ working in inside sales and later as an outside salesman, having a successful career at Star I had the desire with a friend to start our own fastener distribution company in 1980 named: Divspec, Kenilworth, NJ. This was a successful adventure but ended in 1985 with me starting Melfast in August 1985 and have stayed competitive and successful to date. Melfast serves the OEM market with approximately 400 accounts nationally.

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