Identification and AN Specification Overview In the end, you should be able to: Distinguish aircraft hardware from common hardware, Know the AN numbering convention, Be able to match a fastener to its AN number, Select the proper hardware from a blue print drawing, Be able to order hardware from a supplier, Know where to find AN information. Aircraft Hardware “Hardware” is the term used describe the various types of fasteners and small items used to assemble aircraft structures. Only hardware with traceability to an approved manufacturing process or source should be used. Threaded fasteners and rivets are the most commonly used fasteners. AN Hardware Includes Bolts Fittings Nuts Clamps Washers Bushings Screws Angle Brackets Cotter Pins Sheet Metal Screws Rivets Cowling fasteners Much more Bolts Nuts Washers Screws Cotter Pins Rivets Specification Conventions AN – Air Force / Navy NAS – National Aerospace Standards MS – Military Standards AMS – Aeronautical Material Specifications SAE – Society of Automotive Engineers MIL – Military Specifications This Lesson AN Specifications Was the primary standard in 1946. Still widely used today for most hardware. Bolts, Washers, Nuts, Cotter Pins Occasional references to NAS and MS specifications. NAS and MS has more fasteners than AN. Conversion tables available for cross references. AN Specifications - Overview AN3 - AN20 – Standard Bolts AN21 - AN36 – Clevis Bolts AN42 – AN49 – Eye Bolts AN73 – AN81 – Drilled Head Bolts AN310 – Castle Nut AN315 and AN335 – Plain Nut AN960 and AN970 – Washers AN935 and AN936 – Lock Washers AN380 – Cotter Pins (Standard) Bolts Most bolts used on aircraft are General-purpose Internal-wrenching Close-tolerance On the Aeronca Champ, most are General Purpose. Bolt Materials Standard Aircraft Bolts High-strength type 4037 or 8740 alloy steel. Cadmium plated for corrosion resistance. Minimum tensile strength 125,000 PSI. Only specific bolt head markings allowed. Bolt Materials Common Home Depot bolts (non-aviation) Made of a low carbon (mild) steel. No corrosion resistance. Low tensile strength; about 55,000 PSI. Identified by lack of proper AN markings. Often have coarse threads. Aircraft Bolt Identification Bolts are identified by markings on the bolt heads. Denote the materials of which the bolt is made. Standard vs. special-purpose bolts. Sometimes includes the manufacture. * Usually a ‘ ’ or an ‘X’ Challenges Keep your bolts separated to avoid confusion. Know your sources. Not always easy to remember the various markings. Need a chart to know the various markings. 43.13-2B Bolt Terminology Length – Total distance from under head to the tip. Grip – The unthreaded part. Diameter– Thickness of the bolt. Thread size – Pitch of the thread. Other Bolt Terminology Thread Length Head Thickness Head Width These are fixed sized for most aircraft bolts. AN Bolt Numbering Template AN Bolt – Series Number Standard AN bolts are numbered by the diameter. Numbered in sixteenths of an inch. AN3 – 3/16” diameter (3/16) AN4 – 1/4“ diameter (4/16) AN5 – 5/16” diameter (5/16) AN6 – 3/8” diameter (6/16) AN7 – 7/16” diameter (7/16) …… AN20 – 1-1/4” diameter (16/16 + 4/16) AN Bolts – Diameter vs Thread size Each AN bolt diameter has only one: Thread pitch. Thread length. AN Diameter Threads per Inch Thread Length AN3 32 3/8” AN4 28 7/16” AN5 24 9/16” AN6 24 9/16” AN7 20 9/16” AN8 20 9/16” AN Bolt – Dash Number Dash numbers represent the length of the bolt. Numbered in eighths of an inch. -4 - 1/2” length (4/8) -5 - 5/8” length (5/8) -6 - 3/4” length (6/8) -7 - 7/8” length (7/8) -10 - 1” length (1 + 0/8) -11 - 1 1/8” length (1 + 1/8) -12 - 1 1/4” length (1 + 2/8) ….. -24 - 2 1/2” length (2 + 4/8) AN Bolt – Selecting the Length The grip length should equal the thickness of the materials being bolted together. A nut is not to run to the bottom of the bolt threads. If grip is too long, you can use washers. Do not use more than 1/8” of washers (typically two standard AN washers.) Use next length bolt if needed, which is 1/8” shorter. AN Bolt – Quiz AN3-7 AN6-20 AN4-17 AN5-18 AN Bolts – Safety with Cotter Pin Available with or without shank drilled for cotter pin or undrilled for stop nut application. AN Bolts – Safety with Cotter Pin Add the letter “A” to the dash number for undrilled shank. No letter for drilled shank. AN5-10 AN5-10A AN Bolts – Safety with Wire Available with or without drilled head for safety wire. AN Bolts – Safety with Wire Add the letter “H” to the AN number for drilled head. No letter for undrilled head. (Normal) Not to be confused with AN73 to AN81, which have a deeper head. AN4H-15 AN4-12A AN76-6 AN Bolts – Measuring A standard rule can be used to measure existing bolts. AN Bolts – Measuring Bolt Gauges are an easy and accurate way to measure an existing bolt. AN Bolts - Measuring Ordering AN Bolts AN Nuts – Plain Hex Nuts AN315 – Standard AN316 – Checknut AN Nuts – Plain Hex Nuts Rugged construction and can carry the same high tension load as the popular castle nut. It requires an auxiliary locking device such as a check nut or lock washer. AN316 hex check nuts can carry half the tension load of the AN315 nut. They are used as a locking device for plain nuts, set screws, rod ends, etc. Appears to be the only AN nuts available in both right-hand and left-hand thread. Add R or L after dash number for right-hand or left- hand thread. AN Nuts – Plain Hex Nuts -- Thread Direction AN315-4R -- Dash Number AN Nuts – Plain Hex Nuts AN Nuts – Castle Nuts AN310 – Thick nut used for tinsile loads AN320 – Thin nut used only for shear loads AN Nuts – Castle Nuts Fabricated from steel & cadmium plated. The slots in the nut accommodate a cotter pin for safety purposes. AN310 castle nuts are used with drilled-shank bolts, clevis bolts, eye bolts and studs. The thinner AN320 castellated shear nut has half tensile rating of the AN310 nut. AN320 is used with clevis bolts & threaded taper pins which are subject to shearing stress only. AN Nuts – Castle Nuts AN310-5 -- Dash Number AN Nuts – Castle Nuts AN Cotter Pins AN380 - Cadmium plated low-carbon steel AN381 - Corrosion resisting steel Now MS24665 AN Cotter Pins AN380-2-8 -- Length ( 1/4” ) -- Diameter (1/32” ) AN Cotter Pins AN Nuts – Elastic Stop Nuts AN365 – Standard AN364 – Thin for shear loads only. AN Nuts – Elastic Stop Nuts Has a fiber or nylon insert locked into the end of the nut, with a hole slightly smaller than the diameter of the bolt. Screws down freely until the nylon is reached, then a wrench is required. Should not be used in applications where the nut and bolt are subject to rotation. To ensure that the nylon-insert grips all the bolt threads, the complete chamfer on the end of the bolt must stick out beyond the nylon-insert. Should not be used where temperatures exceed 250 degrees. AN Nuts – Elastic Stop Nuts AN365-440 -- Dash Number (Bolt size) AN Nuts – Elastic Stop Nuts AN Washers AN960 standard washers AN970 large washers Standard washers are 1/16”. Some available at 1/32”. AN Washers AN960 Provides smooth bearing surface for nut, Serves as shims to obtain the correct grip length for a bolt and nut assembly, Prevents sharp edges under lock washers from damaging material clamped. AN970 Much larger outside diameter, Used when bolting wood surfaces together, Spreads force applied by bolt and nut over larger area of the wood to prevent crushing. AN Washers AN960-416 AN Washers AN970-4 Practice Except as a last resort, do not torque a bolt by turning it. Elastic stop nuts may be reused many times, certainly until the fiber has lost its locking friction or has become brittle with age. If you can turn the nut up all the way with your fingers, replace it. Practice Since bolt lengths are made in 1/8" increments, washers may sometimes be necessary to obtain the correct grip length for a bolt that is a little too long. A maximum of two standard 1/16" thick washers are sufficient to correct for a slightly long bolt. If not, use the next size shorter bolt. Practice No self-respecting homebuilder will ever allow himself to be caught using a pair of pliers or adjustable wrench to tighten an aircraft nut. AN Hardware Questions? Thank You.
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