Design Problem (Wine Key, Cork Screws)

[winer]

Pardon my ignorance, but what is a "wine key"? I know corkscrews, but have not heard the term "wine key".
In my opinion, the plunger portion of a corkscrew (the part that goes into the cork itself) is too narrow. Many times I have had corks break, because they were too dry. It seems to me that that would be less likely to happen, if the diameter of the plunger was just slightly smaller than the diameter of the neck of the wine bottle.