Carriage Bolts

Carriage Bolts

ASTM A307-Grade A

Carriage bolts are used to fasten metal to timber.  The square shoulder under the rounded head helps hold the bolt in place once tightened.  Carriage bolts come in a variety of sizes and materials such as:

 Zinc-plated:  Better corrosion resistance Grade 5 Steel:  Most commonly used in automotive industry Stainless Steel 18-8:  Most common in hardware.  Comprised of 18% chromium and 8% nickel Hot dipped galvanized: Thickest coating offering high corrosion resistance Silicone bronze:  Primarily used in marine environments because of its superior corrosion resistance.

Below are the ANSI B18.5 standard specifications for Carriage Bolts.  We carry the largest inventory of bolts in South Florida.  Contact us today at (305) 885-1717 or email  We’re happy to assist you with all your fastener needs.

Carriage bolts with UNRC-2A threads can be furnished in two different styles: square-neck carriage bolts in diameters from 1/4″ to
3/4″, inclusive and short square-neck carriage bolts in diameters from 1/4″ to 5/8″ inclusive.

Dimensional data for both styles are shown below.
Minimum Thread Length

The formula for determining thread length is, Bolts 6″ and shorter, 2 diameters plus 1/4″. Bolts over 6″ 2 diameters plus 1/2″. If bolts
are too short to apply the formula, the thread will be extended as close to head as possible.

Square-neck Carriage Bolt Dimensions (in.) ANSI B18.5

M18 FUEL™ 3/8″ Compact Impact Wrench w/ Friction Ring Kit

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