Costco had 100-gram gold bars for $7,600. They sold out in less than a day.

• Costco's largest gold product is a 100-gram bar from PAMP Suisse that last sold for $7,599.99.
• The jumbo-sized bar was briefly available this week, but sold out in less than a day.

Costco has been selling gold and silver at a rate of $200 million per month, per analyst estimates, and it's showing no signs of slowing down.

Look no further than this week's sell-off of the company's largest gold product: 100-gram bars of 24-karat gold from PAMP Suisse that last sold for $7,599.99.

Weighing as much as three and a half standard coins, the two-square-inch slabs cost as much as a high-mileage used car.

The price didn't dissuade gold buyers, who snapped up the stash of 100-gram bars in less than a day. It's unclear how many units were in this release, but the product listing shows dozens of reviews from verified customers.

As one review pointed out, Costco's 2% rewards for Executive membership, plus 2% from Costco's credit card translate to some big bucks on such a large purchase.

In this instance, the combined rewards would come in around $300 — not a bad windfall for converting dollars into gold, assuming prices hold.

Because Costco prices its precious metals so close to the market spot price, the rewards can make the deal extremely competitive.

At these rates, it's unlikely that Costco is making much profit from its precious metals business, but that might not matter for the company right now.

Between the e-commerce cheat code of routing hundreds of millions of dollars through online sales, attracting new members, incentivizing existing members to upgrade, and boosting the appeal of the credit card, there are plenty of benefits for Costco to enjoy.

Costco executives often remind investors that "we're a top-line company" — referring to their dedication to growing sales rather than maximizing profits — and nothing drives that idea home quite like selling through stacks of $7,600 gold bars in less than a day.