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The National Rifle Association has a wine club. Why? Almost certainly due to a cardinal rule of membership organizations: Offer as many benefits as possible to put glue on those members, even if the glue has nothing to do with its primary mission. Members who leave are often hard to replace, which adds to marketing expenses. A low churn rate of members makes adding new ones easier.

The NRA pitch:

A Special Offer from the Official Wine Club of the NRA- 12 Wines for Under $7 a Bottle

It’s an exclusive, first-time offer and an unbeatable value: “Lowest Price Available — Save $110. World’s Finest Wines, a Vintner’s Reserve Table Top Opener — Plus Tasting Notes.” All wines are guaranteed, and there’s no obligation to purchase more.

The practice is not very different from what credit card companies do, or public company retailers who have memberships, like Amazon.com Inc. (NASDAQ: AMZN) or Costco Wholesale Corp. (NASDAQ: COST). Be a member, get a deal. And more deals and more. The organizations measure to see the point at which adding things to keep people attached has reached a profit peak. At that point, it may make sense to taper off, unless there is a strategic reason to add more people.

The NRA’s closet cousin in these approaches is the AARP. Insurance, for life and health (in the NRA’s case guns). A Visa Inc. (NYSE: V) card. Prescription drug discounts. Hotel and car rental discounts.

The NRA and AARP have enough members that these organizations can negotiate favorable deals. Each can bring in millions of potential customers. Those discounts are passed along to members — more glue.

The NRA Wine Club. Clever, but with plenty of precedent.