National Aerospace Standard 3350
The Symmetry Bolt has been laboratory tested to the requirements of NAS 3350. Based on the following test conditions, NAS 3350 tests the bolted joints as an assembly experiencing the vibration as a whole. The Symmetry Bolt is also tested for standard tensile strength requirements to ensure that the special thread form is capable of holding the same load as a standard thread form bolt of the same material.
NAS3350 Testing Conditions
| Vibration Frequency | 1780 cycle per minute |
|---|---|
| Vibration Stroke | 11mm |
| Impact Stroke | 19mm |
| Vibration Direction | Horizontal |
| Test Duration | 17 minutes |
Symmetry Bolt Conditions
| Size | M8, M10, M12, M16 |
|---|---|
| Strength | 8.8 |
| Surface Processing | None |
| Tightening Torque | See the below chart. |
Standard of Acceptance
The bolt and nuts should not slide more than one rotation.The bolt should not exhibit any visible breakage or cracks after the test is completed.
Test Results
Symmetry Bolts completed the vibration period of 17 minutes and exhibited neither rotation nor cracks.
Removal torque after testing indicate jam nuts tightened as vibration continued and blocked main nuts to come loose.
| Tightening Torque(Nm) | Removal Torque(Nm) | Torque Increase | |||
|---|---|---|---|---|---|
| Right Hand Thread Main Nut |
Left Hand Thread Jam Nut |
Right Hand Thread Main Nut |
Left Hand Thread Jam Nut |
Left Hand Thread Jam Nut |
|
| M8 | 20.00 | 6.00 | 26.30 | 11.25 | 187.5% |
| M8 | 25.00 | 4.00 | 30.00 | 6.60 | 165.0% |
| M10 | 50.00 | 10.00 | 26.55 | 22.00 | 220.0% |
| M12 | 80.00 | 25.00 | 72.30 | 28.70 | 114.8% |
| M12 | 70.00 | 15.00 | 34.90 | 31.30 | 208.7% |
| M12 | 75.00 | 20.00 | 47.90 | 30.30 | 151.5% |
| M12 | 80.00 | 20.00 | 77.50 | 29.10 | 145.5% |
| M12 | 70.00 | 10.00 | 51.50 | 37.90 | 379.0% |
| M16 | 130.00 | 40.00 | 81.00 | 42.80 | 107.0% |
In-House Test
While NAS 3350 testing is quite rigorous, it does not take into consideration real world conditions where the assembly consists of clamped members that are subjected to shock or vibration that oppose each other or are not in sync.
Unlike NAS 3350 testing, our in-house test rig applies a shock and vibration load on the bolted assembly which allows the bolted components to move in relation to each other. The test setup includes an electronic load cell which allows for real time display of clamp load during the test process and an electronic torque meter to measure the installation torque and the breakaway-torque of the installed nuts. The testing was conducted to demonstrate the performance in maintaining clamp load of the Symmetry Bolt as compared to other fasteners. It is important to note that the test is not a laboratory test and does not comply with any particular specification or standard.
During testing the bolted joint settles and clamp load drops about 10 to 15 percent. It then either continues to fall or holds steady. Our results show that after the initial drop the Symmetry Bolt maintains clamp load indefinitely (Figure 1) while standard hex nut, nylon locknut, and nut with jam nut lose clamp load within10 seconds(Figure 2).
Figure1 - Passed test with Symmetry Bolt
Figure2 - Failed test with nylon insert locknut
