What are the differences between a hex cap screw and a hex bolt?

What are the differences between a hex cap screw and a hex bolt?

Hex Cap Screws vs Hex Tap Bolts: What’s The Difference?

Hex bolts, hex caps, hex taps, hex heads…there is so much hex bolt lingo.

A hex “tap” bolt is a term used to describe a fully threaded hex bolt. Many of our customers will use the terms “Hex Tap Bolt” and “Fully Threaded Hex Cap Screw” interchangeably. Remember, that in the U.S., a “bolt” is a fastener that is designed to be used with a nut. A “screw” is a fastener that is designed to be able to be installed by tightening the head.

These terms are often incorrectly used interchangeably. The most basic difference between a cap screw and a bolt is the way in which these fasteners are installed. Technically, a bolt is installed by turning a nut to tighten the fastener, while a cap screw in installed by turning the head of the bolt to assemble and tighten.  Therefore, cap screws are often threaded into a tapped hole on a piece of equipment or machinery or installed in some other OEM application.

The variations between these fasteners are fairly significant both from a manufacturing and dimensional perspective as well as an application standpoint. Generally speaking, hex cap screws are used in precise applications like an OEM setting where tight tolerances are required. Hex bolts are often specified when the mechanical properties are more important than dimensional tolerances, like the construction industry. For example, SAE J429 Grade 2 is typically provided as a hex cap screw, whereas ASTM A307-A is a common hex bolt specification.

Below is an overview of some of the specifics these fasteners are required to meet.

Hex cap screws

Flat washer facing under the head that meet specific tolerances as described under ASME B18.2.1-1996.

They will usually be manufactured by a cold-heading process (large runs of standard sizes) or turned CNC operation.

A radius under the head at the shank.

Body diameter of plus nothing, minus .011″ for an 1-1/4″ diameter fastener.

Some common fastener specifications unless otherwise specified: ASTM A449 and SAE J429 Grade 2, 5, and 8.

Hex bolts

A die seam across the bearing surface is permissible.

The typical bolt is manufactured by hot-forging process.

Allows a reduced body diameter to be not less than the minimum pitch diameter of the thread.

Some common fastener specifications unless otherwise specified: ASTM A307A, A354, and F1554.

This list is not inclusive, but represents some of the differences between these two designations. There is flexibility to use other materials, grades, and bolt standards as agreed by manufacturer and purchaser. So, be cautious when ordering bolts make sure you are clear about whether your projects requires cap screws or bolts.

In summary

Tap bolts have threading all the way down regardless of their size. Hex cap screws may have a shoulder in longer sizes, which makes them stronger. Both are typically installed with a nut and designed to be driven by a wrench or socket driver. And last but not least, if a hex cap screw is small enough to lose its shoulder it can also be considered a tap bolt. In smaller sizes, they are the same but once a unthreaded shoulder starts, become different bolts. Browse our entire selection of hex bolts.