How To Determine Nut Strength
WARNING: This page is about a different car, the 2005 Lexus RX 330. However, it is still accessible from the selected car via links, so may be relevant.
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HINT:
Use the nut with the same number of the nut strength classification or the greater than the bolt strength classification number when tightening parts with a bolt and nut.
Example: Bolt = 4T
Nut = 4N or more