GregP
Major
We think they are mostly offshore. Popular belief is China, but I don't know of anyone who can confirm this, so it's probably just earwash and some China-bashing.
Still, SOMEBODY is selling counterfeit aviation grade bolts in both Metric and SAE. So we just buy from known good sources.
If you look in a Mechanical Engineess Handbook, converting torque to tension isn't all that difficult, and figuring the tension taking into account the diameter oif the bolt also isn't all that difficut. Converting 125,000 psi tension into a value for an AN4 or whatever bolt isn't too bad either. So anyone can do the test. Any proper aviation grade bolt SHOULD pass the test.
I've also had the bolt pass fine, but the nut failed. You have to look at the specs for the nuts to determine what they should pass. AN4 is the smallest aviation grade bolt that is used for structural reasons, so that's as small as I have tested.
Believe me, the British bolts pass just fine and so do the metric ones from WWII. The conterfeits are universally newer stuff. Maybe that's why so many poeople clean up the old hardware and send it out for cadmium plating ... they know they have good hardware.
Or maybe they're just cheap! I know of at least 10 people who collect the old hardware, soak it in parts cleaner or some other solvent, and send it out for cad on a regular basis. In the past, I helped restore an old jet fighter to remain unnamed. That's what we did and is it was due more to being unable to find the proper bolts new than to being cheap. Some sizes and lengths apparently haven't been made in a long time.
I found one source who quoted me $5 each for countersunk nutplates with a nut size for number 10 screws. We needed about 1,000. Then we found another dealer who sold us a lot of 2,000 for a total of $600! So ... the prices vary wildly. The thing is, countersunk nutplates carry some of the structural load and so cannot be replaced with non-countersunk nutplates. Just one example of wild pricing variation and the attraction for counterfeit hardware that can add up to a lot of money and serve as an incentive for counterfeiters.
For instance: say we have an AN4 bolt. The diamter and pitch are therefoire 1/4-28. The bolt thread tensile stress area is found by: As = .7854 * (d - (.9743/n))^2, where d is diameter in inches, n is threads per inch. This workes out to .03637 square inches. The bolt material proof strength (Sp) is supposed to be 125,000 psi. If I wanted to reuse it, I'd set the proof test at 0.75 of proof load, per recommendations in many places.
So .75 * 125,000 * .03637 square inches is 3,410.1 pounds of force, or Fi = .75 * Sp * As.
The Tension can be calculated using T = k * Fi * d, where T is torque in inch-pounds, Fi is bolt clamp load force (3,410.1 pounds as shown above), d is diameter in inches, and k varies with the type of finish. Use .13 for Cad plate, .15 for lubricated threads, .18 for Zinc plated, and .20 for plain dry threads. So, the torque for .75 of proof load for lubricated threads would be: .15 * 3,410.1 * 1/4 = 128 inch pounds.
I set up a spreadhseet for it and thus the calculations are as simple as entering the bolt size.
So for an AN4, the values for .75 of proof load come out to 111 in-lbs for Cad plate, 128 in-lbs lubricated, 153 in-lbs for Zinc plated, and 171 in-lbs for plain dry threads. Values for full proof load are 148, 171, 205, and 227 respectively.
So, to check an AN4, I'd put it in tension and torque to 171 inch-pounds for plain dry threads (111 inch-pounds for cadmium plate). If it holds, you can still use the bolt. If it fails it was counterfeit. If you really want to check the same bolt for counterfeit, go to 227 inch-pounds (148 for Cadmium) and it should make that OK, and fail if you torque it much more. I would not reuse it if I tested it to proof load, but some do.
I mostly use Cadmium threads since our bolts are cadmium plated, not Zinc plated, and I don't lubricate them. The calculation for metric are simple ... I just convert the metric size to inches and run the same calculation. It would not be hard to set up a sheet just FOR metric, but I don't run across that much, so it isn't worth the trouble to me.
By the way, for what it is worth, SAE J429 Grade 2 bolts have a proof load of 55,000 psi for 1/4"to 3/4" diameter. Grade 5 have a proof load of 85,000 psi for 1/4" to 1" diameter. Grade 8 have a proof load of 125,000 psi for 1/4" to 1.5" diameter. But you still cannot use Grade 8 in aircraft. Grade 8 has many more threads than an AN aircraft bolt, and you don't want the threads in the material being bolted together in an aircraft. ASTM A574 Socket Head Cp Screws have a proof load of 140,000 psi for #0 to 1/2" diameter, but again, they have too many threads.
I've also seen Grade 8 quoted as 150,000 psi tensile, 130,000 psi yield, and 120,000 psi proof load.
But AN bolts in size 3 - 8 should be 125,000 psi proof.
If you're going to build or repair an aircraft, use bolts designed for aircraft.
Last, the numbers above are proof loads, not torque applied in aircraft use or maintenance. For that I use my own chart.
Still, SOMEBODY is selling counterfeit aviation grade bolts in both Metric and SAE. So we just buy from known good sources.
If you look in a Mechanical Engineess Handbook, converting torque to tension isn't all that difficult, and figuring the tension taking into account the diameter oif the bolt also isn't all that difficut. Converting 125,000 psi tension into a value for an AN4 or whatever bolt isn't too bad either. So anyone can do the test. Any proper aviation grade bolt SHOULD pass the test.
I've also had the bolt pass fine, but the nut failed. You have to look at the specs for the nuts to determine what they should pass. AN4 is the smallest aviation grade bolt that is used for structural reasons, so that's as small as I have tested.
Believe me, the British bolts pass just fine and so do the metric ones from WWII. The conterfeits are universally newer stuff. Maybe that's why so many poeople clean up the old hardware and send it out for cadmium plating ... they know they have good hardware.
Or maybe they're just cheap! I know of at least 10 people who collect the old hardware, soak it in parts cleaner or some other solvent, and send it out for cad on a regular basis. In the past, I helped restore an old jet fighter to remain unnamed. That's what we did and is it was due more to being unable to find the proper bolts new than to being cheap. Some sizes and lengths apparently haven't been made in a long time.
I found one source who quoted me $5 each for countersunk nutplates with a nut size for number 10 screws. We needed about 1,000. Then we found another dealer who sold us a lot of 2,000 for a total of $600! So ... the prices vary wildly. The thing is, countersunk nutplates carry some of the structural load and so cannot be replaced with non-countersunk nutplates. Just one example of wild pricing variation and the attraction for counterfeit hardware that can add up to a lot of money and serve as an incentive for counterfeiters.
For instance: say we have an AN4 bolt. The diamter and pitch are therefoire 1/4-28. The bolt thread tensile stress area is found by: As = .7854 * (d - (.9743/n))^2, where d is diameter in inches, n is threads per inch. This workes out to .03637 square inches. The bolt material proof strength (Sp) is supposed to be 125,000 psi. If I wanted to reuse it, I'd set the proof test at 0.75 of proof load, per recommendations in many places.
So .75 * 125,000 * .03637 square inches is 3,410.1 pounds of force, or Fi = .75 * Sp * As.
The Tension can be calculated using T = k * Fi * d, where T is torque in inch-pounds, Fi is bolt clamp load force (3,410.1 pounds as shown above), d is diameter in inches, and k varies with the type of finish. Use .13 for Cad plate, .15 for lubricated threads, .18 for Zinc plated, and .20 for plain dry threads. So, the torque for .75 of proof load for lubricated threads would be: .15 * 3,410.1 * 1/4 = 128 inch pounds.
I set up a spreadhseet for it and thus the calculations are as simple as entering the bolt size.
So for an AN4, the values for .75 of proof load come out to 111 in-lbs for Cad plate, 128 in-lbs lubricated, 153 in-lbs for Zinc plated, and 171 in-lbs for plain dry threads. Values for full proof load are 148, 171, 205, and 227 respectively.
So, to check an AN4, I'd put it in tension and torque to 171 inch-pounds for plain dry threads (111 inch-pounds for cadmium plate). If it holds, you can still use the bolt. If it fails it was counterfeit. If you really want to check the same bolt for counterfeit, go to 227 inch-pounds (148 for Cadmium) and it should make that OK, and fail if you torque it much more. I would not reuse it if I tested it to proof load, but some do.
I mostly use Cadmium threads since our bolts are cadmium plated, not Zinc plated, and I don't lubricate them. The calculation for metric are simple ... I just convert the metric size to inches and run the same calculation. It would not be hard to set up a sheet just FOR metric, but I don't run across that much, so it isn't worth the trouble to me.
By the way, for what it is worth, SAE J429 Grade 2 bolts have a proof load of 55,000 psi for 1/4"to 3/4" diameter. Grade 5 have a proof load of 85,000 psi for 1/4" to 1" diameter. Grade 8 have a proof load of 125,000 psi for 1/4" to 1.5" diameter. But you still cannot use Grade 8 in aircraft. Grade 8 has many more threads than an AN aircraft bolt, and you don't want the threads in the material being bolted together in an aircraft. ASTM A574 Socket Head Cp Screws have a proof load of 140,000 psi for #0 to 1/2" diameter, but again, they have too many threads.
I've also seen Grade 8 quoted as 150,000 psi tensile, 130,000 psi yield, and 120,000 psi proof load.
But AN bolts in size 3 - 8 should be 125,000 psi proof.
If you're going to build or repair an aircraft, use bolts designed for aircraft.
Last, the numbers above are proof loads, not torque applied in aircraft use or maintenance. For that I use my own chart.
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