Meat grinder plate hole sizes determine the texture of the ground meat you produce. 

Most hamburger meat is 1/8"

In most parts of the US, hamburger meat is ground using an 1/8" hole grinder plate. 

Here are some other common sizes and uses:

• 1/8" - Hamburger meat
• 5/32" - Hamburger meat in Texas
• 3/16" - Sausage
• 3/8" - Chili meat
• Kidney - Beef stew

The 1/8" is the most common plate you'll find behind most meat counters.  In fact, many butchers will keep a couple of these around for safe measure.  The 3/8" and 3/16" are the next most common sizes.  

The images below show the approximate texture of ground meat produced from specific hole sizes.