Missing threads not a problem.

Dear Half-Mast,

We have some concerns about; MWO 9-2320-279-20-9, Installation Instructions For Bolt Together Wheels For the M977-series HEMTTs.

After installing the bolt-together wheels, we've found that there are zero stud threads showing past the lug nuts after correct torque is applied. Because of that, it's obvious that the studs and wheel nuts do not meet the criteria spelled out in TB 43-0218, Inspection, Use and Tightening of Metal Fasteners Used on Tank-Automotive Equipment.

Para 7b on Page 6 says, "In all installations, bolts, studs and screws must extend through the nut at least a length equivalent to two complete threads. This applies to both self-locking and plain nuts."

Is there a longer wheel stud that we should be using when applying this MWO? Of are the current studs OK, even with no threads showing?

MSG J.J.K.

Master Sergeant J.J.K.,

Good questions! in this particular case, however, TACOM says the criteria from TB 43-0218 does not apply.

The key to any lug nut/stud combination is not the visual check, but the requirements for clamping force and torque retention. It doesn't matter how many threads protrude outside the lug if the clamping force cannot be met or the lug will not hold the torque.

To ensure proper torque retention, the lug nut height must be at least 80% of the stud's diameter. The current HEMTT design exceeds this requirement, so there's no need for the studs to extend past the lug nuts.

Before the MWO was released, TACOM put HEMTTs through multiple tests, including several brake, shock and vibration tests and more than 25,000 test miles. There were no incidents of lug nuts loosening during these tests.

Today, more than 2,000 HEMTTs are currently operating with the bolt-together wheel configuration with no problems reported.