When I installed my TF rack I reused the existing extenders as they seemed in good condition. They went right up to the shoulder on the extender into the new TREs so effectively self locked by the shoulder touching the TRE. No lock nut against the TRE. The lock nut was used on the rack thread tightened up the extender. Rack is in front of the king pin line so toe out if too long. I found there was plenty of adjustment and could have gone toe in or toe out so my extenders seem to be the right length. Pics:
From when I refurbed the front suspension in 2015, still with the old Metro rack:
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rack extender.jpg [ 320.9 KiB | Viewed 2911 times ]
A few weeks ago with my newly fabricated ARB and TF rack:
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near side complete.jpg [ 275.91 KiB | Viewed 2911 times ]