Wash 8-10 pint-size canning jars, their lids and the screw tops. Fill a water-bath canning pot about half full and bring the water to a boil. Lower the jars into the boiling water and sterilize for 10 minutes.
Stir together the vinegar, salt and water and bring it to a boil in a large pot. Lower the temperature, cover and simmer until ready to use.
Wash, de-stem and trim the beans to fit into jars with 1/2 inch head room. Stand the beans up in the jars.*
Peel the garlic.
Place 2 garlic cloves, 1-2 fronds of dill, 1 tablespoon of mustard seed and 1/8 teaspoon or more of red pepper flakes into each jar with the beans.
Place the lids in a bowl or dish that can hold boiling water. Boil 3-4 cups of water and pour it over the lids.
Using a funnel, ladle the salt/vinegar brine into the jars to 1/2 inch from top.
Dampen a clean cloth or paper towel and wipe the rim of each jar. Place the hot lid on top and screw the band on.
Place the jars in the rack of the water-bath pot of boiling water and gently lower them into the pot. The water should cover the jars by an inch or so. Cover and boil for 5-15 minutes**
Remove the jars with a jar lifter and let them cool completely on a cooling rack. The lids should seal as they cool. If they don't, re-boil for 5 minutes and let them cool completely. If a jar still doesn't seal, put it in the refrigerator after it has cooled and eat that one first!
Store in cool dark place. Dilly Beans will keep for 12-18 months.
*You can par-boil the beans at this point, it you want. Boil for 2-3 minutes and then dunk immediately in very cold or ice water to stop the cooking.
**Boil for 5 minutes if you live between 0-1,000 feet altitude; 10 minutes 1,001-6,000 feet; and 15 minutes above 6,000 feet.