Gas tanks - revisited

I think you are being confused by their misleading generic ad text.

55-57 tanks and senders don't have an o-ring and lock ring on the sender opening. They have a gasket and screws.

In the 60s GM went to the o-ring/lock ring feature for the sender. That is what the ad is referring to.

If a 55-57 tank were to have a lock ring, you'd have to have a sending unit for a lock ring.

Notice that the ad says they supply the lock ring/o-ring and gasket/screws. No tank needs both.

I think almost every (maybe every) 55-57 replacement tank on the market is from the Canadian company Spectra.

So you need to buy based on the bottom line of price + shipping.

Based on your two links, the $112 tank + $35 shipping = $147, so it's $33 cheaper than the other tank.

$112 is a good price.