Advice from someone who deals with bolted joints as part of their job.
Hardware:
SAE Grade 8 | Metric Class 10.9 or better hardware.
Coating:
1. Chromate on Cadmium preferable but near-impossible to get for metric.
2. Chromate on Zinc is an okay substitute and should be easy to get in metric.
3. Bright is acceptable in a pinch.
4. NEVER black phosphate.
Locking Features:
1. The best locking feature is lock-wire or Safety cable.
2. Prevailing torque castellated lock-nuts with distorted threads and a cotter pin is the next best.
3. Realistically, prevailing torque lock-nuts with distorted thread and loctite is the best one can do for replacement hardware as 1 and 2 require some pre-planning on the greater assembly.
4. Prevailing torque lock-nuts with distorted threads are better that lock-nuts with plastic locking feature.
5. Do not rely on lock-washers.
6. Locking features on external threads (strip, patch, or dot) are okay, but have wildly varying prevailing torques.
7. If upgrading to bolted joint with locking features: in order to maintain factory clamp specs, the locking feature's prevailing torque (how much torque is required just to turn the nut) will need to be measured and added to the factory torque spec.
8. While mil-spec locking hardware should be good up to 5 times of use, unless you know for certain how many times hardware has been stressed, it is best to replace it.
Hardware:
SAE Grade 8 | Metric Class 10.9 or better hardware.
Coating:
1. Chromate on Cadmium preferable but near-impossible to get for metric.
2. Chromate on Zinc is an okay substitute and should be easy to get in metric.
3. Bright is acceptable in a pinch.
4. NEVER black phosphate.
Locking Features:
1. The best locking feature is lock-wire or Safety cable.
2. Prevailing torque castellated lock-nuts with distorted threads and a cotter pin is the next best.
3. Realistically, prevailing torque lock-nuts with distorted thread and loctite is the best one can do for replacement hardware as 1 and 2 require some pre-planning on the greater assembly.
4. Prevailing torque lock-nuts with distorted threads are better that lock-nuts with plastic locking feature.
5. Do not rely on lock-washers.
6. Locking features on external threads (strip, patch, or dot) are okay, but have wildly varying prevailing torques.
7. If upgrading to bolted joint with locking features: in order to maintain factory clamp specs, the locking feature's prevailing torque (how much torque is required just to turn the nut) will need to be measured and added to the factory torque spec.
8. While mil-spec locking hardware should be good up to 5 times of use, unless you know for certain how many times hardware has been stressed, it is best to replace it.
