A carriage bolt (also called coach bolt and round-head square-neck bolt is a form of bolt used to fasten metal to metal or metal to wood.

It is distinguished from other bolts by its shallow mushroom head and the fact that the cross-section of the shank,though circular for most of its length (as in other kinds of bolt), is square immediately beneath the head.12lThismakes the bolt self-locking when it is placed through a square hole in a metal strap.This allows the fastener to be installed with only one tool, a spanner or wrench, working from one side.The head of a carriage bolt usually is a shallow dome.The shank has no threads; and its diameter equals the side of the square cross-section.

The carriage bolt was devised for use through an iron strengthening plate on either side of a wooden beam, the squared part of the bolt fitting into a square hole in the ironwork. t s common to use a carriage bolt to bare timber, the square section giving enough grip to prevent rotation.

The carriage bolt is used extensively in security fixings,such as locks and hinges, where the bolt must be removable from one side only. The smooth,domed head and square nut below prevent the carriage bolt from being unlocked from the insecure side.

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Parameters 

Application

1.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.

2.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.

Features

Nuts and bolts probably share the same chemistry as that of salt and pepper. While nuts are hardware fasteners, featuring threaded holes, the stainless steel carriage bolts are fasteners, featuring round and flat heads without any thread. These are tightened by a wrench onto a surface and the process is completed by fastening the bolt at the other end. 

Such type of fastener is usually found in wooden chairs or couch, which hold two separate wooden pieces. Not only in the furniture, but these fasteners are widely used in iron and steel industries as well. The heavy duty screws and bolts are specially designed to withstand heavy weights and offer safety and durability. The bolts are available in three primary designs and the carriage type is one of them.