Where do I get a corkscrew I can use on a double magnum?

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Dear Dr. Vinny,
Where do I get a corkscrew that is able to open a double magnum or larger bottle?
—David, Holmdel, N.J.
Dear David,
Corks in large-format bottles might have a bigger diameter, but they are usually normal length, and a standard corkscrew should work just fine.
For a job like this, I'd recommend a waiter's corkscrew (the one that resembles a Swiss Army knife), so that you have plenty of control. Use one with a thin, pointy worm, put it in the center of the cork, and twist it inside (as parallel to the bottle as you can get it), until there's about a turn of the worm still visible. Then put the fulcrum's notch at the edge of the bottle, and while holding the fulcrum to the bottle, gently raise the cork just a little bit. Turn the screw in a little more, pull the cork a little more. Once you get the cork moving away from the bottle, you should be fine.
If that doesn't happen, and the cork isn't budging from the bottle—only crumbling around the corkscrew—try an Ah-So, which slides two prongs on either side of the cork, and with a gentle back-and-forth rocking motion, you should be able to get your cork out intact.
—Dr. Vinny