I bought a set of Red Top Optimas a while back for my MegaCab (have them on the 99 as well). They didn't come with adapters. I gave the company a call, and they shipped me a free set of the adapters within a couple of days (same state as call center) to make them work with my factory hold downs. Here are a few pics.
Bought two of these:
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Called and they shipped me two each of these:
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Took a pair of channel locks and squeezed the adapters down into the clips.
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A pic of the adapters installed:
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Pics of the batteries installed... With no bungee cords... LOL :-laf And they hold in very nicely.
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And a close up of one of the adapters on the installed batteries:
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Bought two of these:

Called and they shipped me two each of these:


Took a pair of channel locks and squeezed the adapters down into the clips.


A pic of the adapters installed:

Pics of the batteries installed... With no bungee cords... LOL :-laf And they hold in very nicely.


And a close up of one of the adapters on the installed batteries:
