In a saucepan, combine the vinegar, salt, water, garlic, sugar, mustard seeds, and peppercorns. Bring it to a simmer.
While waiting for the ingredients to simmer, slice the cucumbers about 1/4" thick.
Place a few sprigs of dill into each jar and tuck them against the side.
Once the ingredients in the saucepan come to a boil, stir well and remove from heat. Let it cool to room temperature.
Once the brine has cooled, divide the liquid between the 3 jars. Also, divide the mustard seeds, peppercorns, and garlic between the jars.
If the liquid didn't fill the jars, add more cucumber slices or top off with water.
Screw the lid on and put the jars in the fridge for 48 hours. After 48 hours, taste the pickles. If they're too vinegary but lacking garlic dill flavor, let them sit for another day.
Notes
Pickling cucumbers can be used if available, but English cucumbers work well too. Regular US cucumbers tend to get mushy, so they're not recommended for this recipe.