Clevis, Countersunk and other bolts
Previous pages discussed the standard AN airframe bolt AN3 - AN20. We continue here with the Clevis bolt (AN21 - AN36) usually used in shear applications and some countersunk bolts like the AN509. We also give some attention to the eye bolt and the washer head screw.
The countersunk bolts are used in places where the standard AN bolt would not fit due to its larger head. They are sold in different lengths and thread sizes.
These bolts are to be used in applications subject to shear stresses only, and are often used as mechanical pins in control applications like throttle cable connection to the carburettor or fuel injection system of an engine. A clevis is a U-shaped fitting similar to a shackle. The clevis is not to be used in tensile load applications.
Clevis bolts have a slotted brazier type head and are special-purpose bolts for use where a large shearing stress occurs (never in tension). Minimum tensile strength is 125,000 PSI. You can buy them drilled or undrilled in the shank, designated with an A for an undrilled bolt.
A slightly different version is the clevis pin (MS20392 or AN392 - AN406). With the Clevis pin you do not use a bolt but a cotter pin or ring to safety the pin. Whereas with the clevis bolt a castle nut and cotter pin would be used and in certain situations a self locking nut can be applied as well.
Diameter and length of a clevis pins is designated by the number after the dash in 1/32 inch. For example a AN392-9 is 1/8 dia by 9/32 inch length. The AN393 is a 3/16 diameter pin with the number after the dash indicating the length in 1/32 inch, thus a AN393-9 is 9/23 inch and a AN393-11 is 11/32 inch. An AN394- is 1/4 inch diameter.
The Clevis bolt is made of a nickel steel alloy, SAE 2330.
For the AN12 - AN23 bolt the second digit denotes the fine thread machine screw size, ie AN21 = 6-40, AN22 = 8-36 and AN23 = 10-32. For the AN24 - AN36 bolts the second digit denotes the diameter in 1/16 inch increments. For example the AN25 has diameter of 5/16 inch.
The number following the dash indicates the length of the bolt in 1/16 inch. AN21-9 indicates a length of 9/16 inch and an AN21-26 is 26/16 inch or 1-5/8 inch.
The thread size is Class 3NF.
The AN509 or MS24694 is a 100° countersunk bolt with flat head structural machine screw. Normally used where a normal AN bolt would give clearance problems due to the thickness of its head.
Thread sizes are 8-32 (8R), 10-32 (10R) and 1/4-28 (416R) where the length is given as the first digit following the R in xx/32 inch. For example: the AN509-10R10 has a thread size of 10-32 with a length of 21/23.
Countersunk AN505R bolt
The same type of bolt as the AN509 but the threads go all the way up to the head and the head is 82° countersunk. Also called MS35190 and can be had in multiple lengths from 1/4 inch to 5/8 inch. Thread size is 4-40, 6-32 and 8-32.
Countersunk AN507R bolt
The AN507R or MS24693 is a 100° countersunk flat head machine screw with a thread size of 4-40, 6-32, 8-32, 10-32 and 1/4-28 and its length varies from 1/4 to even 2 inch for the 8-32 thread size.
These eye bolts are special purpose bolts and used where external tension loads are applied or expected. The eye of the bolt is designed for attachment of such things as a turnbuckle fork, a clevis or a cable shackle. Minimum tensile strength 125,000 PSI.
Eye bolts are made with either drilled or undrilled shank, and use the letter "A" after the dash number to designate an undrilled shank
The bolt must be aligned with the load. If the load is applied sideways the bolt may bend or break. Use washers to make sure that the bolt makes firm contact with the surface. The nut must be torqued properly.
Washer head bolt
The AN525 washer head is a structural machine screw with a built in washer and is available in lengths from 3/8 to 2 inch with grip length from 1/32 to 1-19/32 inch. Thread sizes range from 8-6 to 8-32, 10-6 to 10-32 (AN3 size) and for the 1/4-28 416-6 to 416-32 (AN4 size). Add 'D' before first dash number for AL alloy screws and add a 'R' between first and second dash number for recessed head screws.
AN525-10-6 is a .190-32 slotted head screw steel, 3/8 inch long with a 1/32 inch grip.
AN525-10R6 is a .190-32 recessed head steel screw, 3/8 inch long with a grip of 1/32 inch.