The Key Lime is known as a real Florida treat. However, due to disease and weather disasters, Florida's commercial crop was wiped out years ago. the key lime is a specific variety of lime. It is not exclusive to the Keys. It was brought there years ago and became naturalized.

The key lime is in a class all of its own. Much smaller than regular "Persian" limes, the key lime ranges in size from a ping-pong ball to a golf ball (about 10cm to16cm in circumference). The peel is thin, smooth and greenish-yellow when ripe. The flesh is also greenish-yellow and full of highly polyembryonic seeds (two or more plants from one seed). The interior is divided by 10 to 12 segments, quite juicy and has a higher acidity than regular Persian limes. Key limes have a very distinctive aroma, which makes them valuable for culinary use. The tree itself is small and bushy, rarely taller than 12 feet. It is armed with slender, extremely
thorny branches. Some varieties are thorn less, but these have a
much lower fruit yield than than the thorned trees. Its foliage
consists of small, pale green, blunt-pointed leaves.

Today, the commercial lime industry based on the key lime takes place in areas other than the United States. Key limes are generally not
harvested commercially in the United States due to the ferocious nature of the trees. There are exceptions, but the primary source of commercial key lime juice available in the United States comes from concentrates. The juice is shipped in large drums, it is then reconstituted, "preserved", and sold from some tropical location (usually the Florida Keys). 
In foreign locations, most of the crop is used fresh in limeade, mixed drinks and iced tea, squeezed onto seafood or other foods to bring out the flavor. It is also used in bottled lime juice and carbonated beverages. The principal byproduct is lime oil, used in cosmetics and flavoring. The Key Lime has pale yellow zest, and a light yellow green pulp. It is intensely flavorful and the juice is used for drinks, and desserts, such as the famous Florida Key Lime Pie.

http://www.keylime.com/

http://www.naples.net/media/keylime.html
The yield for juice is 42% per fruit.

http://keylimepiecompany.com/products.htm