Using Aircraft Quality Hardware on Your Vehicle Part 3

Wayne Scraba

1 Mar 2017

Click Here to Begin Slideshow Over the past two issues, we examined high quality AN (aircraft) bolts and fiber as well as all-metal lock nuts. Another common airframe hardware item is the castle nut. These fasteners are most often used for tension loads. Castle nuts are used with drilled shank bolts, clevis bolts and eye bolts. The slots in the nut accommodate a cotter key or pin (or lock wire), obviously for safety purposes. Castle nuts are fabricated from steel and finished with cadmium plating. Corrosion resistant castle nuts are also manufactured, and have a letter "C" added to the AN number suffix. The "C" designates "stainless.” Two types of castle nuts are generally available – standard and thin. A thin AN320 castellated shear nut has half the tensile strength of an AN310 conventional height nut and is used with clevis bolts, which are subject to shear stress only. The dash number that follows the “AN310” or “AN320” prefix indicates the bolt size that the nut fits. If you do some digging at an aircraft supply house, you can also find standard, non-locking nuts. Technically, these have limited use on aircraft structures. They mandate an auxiliary locking device such as a check nut or lock washer. The check nut is a half-height nut (something we in the racing/high performance world would call a "jam nut") used to hold a plain nut in place - an AN316. If a lock washer is used, a plain washer must be placed under the lock washer to prevent damage to the surface. These nuts are manufactured with either a right or left hand thread. Like the self-locking nuts, these fasteners are available in a wide range of thread sizes (sizing follows the AN description shown earlier). When it comes to plain flat washers, the main task is to provide a shim when needed, let them act as a smooth load-bearing surface, and adjust the position of castle nuts in relation to the drilled hole in a bolt. Plain washers are also used under a lock washer in order to prevent surface damage. The most common aircraft flat washers are "AN960" examples. They are manufactured in two thicknesses - regular and one-half thickness. The dash number following the AN960 indicates the size bolt for which they are used. The numbering system is slightly different from the balance of aircraft hardware. For example, an AN960-616 washer is used with a 3/8-inch bolt (616 = 6/16 or 3/8"). There's more too: If you encounter an "L" following the dash number, that signifies a thin or "light" washer. A "C" suffix indicates a stainless washer. Another washer you might come across is an "AN970.” The dash number is completely different, simply because it is a large area flat washer typically used with wood or composite applications. The wider surface area is designed to protect the wood or composite. There are several other types of washers found in aviation that can find residence in a high performance automotive application. As an example, the aviation industry uses lock washers with a split ring, internal tooth lock washers or external tooth lock washers (internal/external tooth lock washers are sometimes called "shake proof" washers). When considering lock washers, the aircraft industry notes they may be used with bolts or machine screws, but should only be used when a self-locking nut or castellated type of nut is not applicable. In an airplane, they are not to be used to fasten primary or secondary structures. Additionally, they should not be used where they are subject to frequent removal or where corrosion is an issue. A self-locking nut, cotter key or safety wire is much preferred over a lock washer. The most common cotter keys found in light aviation are AN380 as well as AN381. The AN380 jobs are cadmium plated while the AN381 variants are manufactured from stainless steel. Obviously, cotter pins are designed to add safety to bolts, screws and nuts, as well as other pins (they are normally used in conjunction with castle nuts). The dash number used for cotter pins indicates the diameter and the length of the pin. Fair enough, but where do you find such hardware? Typically, AN fasteners are available from aircraft supply houses. From our experience, the biggest high performance friendly source is Aircraft Spruce & Specialty Company. They have three locations: Western USA (Corona, CA), eastern USA (Peachtree, GA) and Canada (Branford, ON), and from our experience they certainly won’t hang up if you need parts for a hot rod or race car. More in the accompanying photos!

Using Aircraft Quality Hardware on Your Vehicle Part 3 — Click Here to Begin Slideshow Over the past two issues, we examined high quality AN (aircraft) bolts and fiber as well as all-metal lock nuts. Another common airframe hardware item is the castle nut. These fasteners are most often used for tension loads. Castle nuts are used with drilled shank bolts, clevis bolts and eye bolts. The slots in the nut accommodate a cotter key or pin (or lock wire), obviously for safety purposes. Castle nuts are fabricated from steel and finished with cadmium plating. Corrosion resistant castle nuts are also manufactured, and have a letter "C" added to the AN number suffix. The "C" designates "stainless.” Two types of castle nuts are generally available – standard and thin. A thin AN320 castellated shear nut has half the tensile strength of an AN310 conventional height nut and is used with clevis bolts, which are subject to shear stress only. The dash number that follows the “AN310” or “AN320” prefix indicates the bolt size that the nut fits. If you do some digging at an aircraft supply house, you can also find standard, non-locking nuts. Technically, these have limited use on aircraft structures. They mandate an auxiliary locking device such as a check nut or lock washer. The check nut is a half-height nut (something we in the racing/high performance world would call a "jam nut") used to hold a plain nut in place - an AN316. If a lock washer is used, a plain washer must be placed under the lock washer to prevent damage to the surface. These nuts are manufactured with either a right or left hand thread. Like the self-locking nuts, these fasteners are available in a wide range of thread sizes (sizing follows the AN description shown earlier). When it comes to plain flat washers, the main task is to provide a shim when needed, let them act as a smooth load-bearing surface, and adjust the position of castle nuts in relation to the drilled hole in a bolt. Plain washers are also used under a lock washer in order to prevent surface damage. The most common aircraft flat washers are "AN960" examples. They are manufactured in two thicknesses - regular and one-half thickness. The dash number following the AN960 indicates the size bolt for which they are used. The numbering system is slightly different from the balance of aircraft hardware. For example, an AN960-616 washer is used with a 3/8-inch bolt (616 = 6/16 or 3/8"). There's more too: If you encounter an "L" following the dash number, that signifies a thin or "light" washer. A "C" suffix indicates a stainless washer. Another washer you might come across is an "AN970.” The dash number is completely different, simply because it is a large area flat washer typically used with wood or composite applications. The wider surface area is designed to protect the wood or composite. There are several other types of washers found in aviation that can find residence in a high performance automotive application. As an example, the aviation industry uses lock washers with a split ring, internal tooth lock washers or external tooth lock washers (internal/external tooth lock washers are sometimes called "shake proof" washers). When considering lock washers, the aircraft industry notes they may be used with bolts or machine screws, but should only be used when a self-locking nut or castellated type of nut is not applicable. In an airplane, they are not to be used to fasten primary or secondary structures. Additionally, they should not be used where they are subject to frequent removal or where corrosion is an issue. A self-locking nut, cotter key or safety wire is much preferred over a lock washer. The most common cotter keys found in light aviation are AN380 as well as AN381. The AN380 jobs are cadmium plated while the AN381 variants are manufactured from stainless steel. Obviously, cotter pins are designed to add safety to bolts, screws and nuts, as well as other pins (they are normally used in conjunction with castle nuts). The dash number used for cotter pins indicates the diameter and the length of the pin. Fair enough, but where do you find such hardware? Typically, AN fasteners are available from aircraft supply houses. From our experience, the biggest high performance friendly source is Aircraft Spruce & Specialty Company. They have three locations: Western USA (Corona, CA), eastern USA (Peachtree, GA) and Canada (Branford, ON), and from our experience they certainly won’t hang up if you need parts for a hot rod or race car. More in the accompanying photos!

Castle nuts are also common in aircraft applications. They are most often used for tension loads. Most aviation castle nuts are fabricated from steel and are cadmium plated.

The slots in a castle nut accommodate a cotter key or pin (or lock wire), obviously for safety purposes.

Here’s an AN bolt coupled with a castle nut and cotter key. This setup or an AN locknut (or a locking nut of some sort) is definitely preferred to a plain nut and lock washer.

Plain nuts are designed for use with either a check nut (or “jam nut”) or with a lock washer. Plain nuts are manufactured with either a right or left hand thread. They’re not commonly used in aviation, at least in any high-stress application.

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