Start your water bath canner in a pot big enough to hold 5 one pint mason jars. The water (and the pot!) should be deep enough once the jars are added there is at least 1 inch of water above the top of the jars. Bring the pot to a boil.
Prepare a brine by bringing 4 cups water, 4 cups vinegar and 1/2c salt to a boil.
While the brine and canner are coming up to a boil, gently wash cucumbers to remove any dirt and nip off both ends. Either leave the cucumbers whole or slice into 1/2inch slices.
At the bottom of each wide mouth pint mason jar, add 1 teaspoon of mustard seeds, dill seeds, coriander seeds, black peppercorns and the dill heads or fresh herb sprigs.
Pack tightly with pickles and a few slices of onion. Top 2 with 2-3 garlic cloves. Be sure to leave 1 inch of headspace above the pickles.
Cover with brine to just submerge the vegetables, being sure to leave 1/2 inch of headspace above the top level of the brine.
Cap and band mason jars to just finger tight and place into boiling water in your water bath canner. Process for 10 minutes for pints (or 15 min for quarts) below 1000 feet of elevation. (15 minutes for pints at 1,000-6,000 feet)
Notes
This recipe makes slightly more brine than you need to can 5 pints of pickles, to make sure you have enough to properly fill all the jars. Store any extra in a mason jar at room temperature for later use.
The spices can also be adjusted without affecting canning safety, based on your preferences.
The salt is not necessary for preservation in this recipe, and can be adjusted to your tastes. Salt levels in pickles are a very personal thing, and I've seen recipes that use A LOT more salt, and just a few that use less. Around 1/2 cup is a good middle ground, but if you like them REALLY salty add 3/4 cup (alternatively, use 1/4 cup for lower salt pickles).
DO NOT use table salt, it has additives that don't work well for canning. Lacking pure canning salt, use kosher salt.
DO NOT adjust the vinegar/water ratio to lower the amount of vinegar. The acidity in the vinegar is what preserves the pickles and makes them suitable for water bath canning. For a more sour pickle, you can increase the amount of vinegar (but never reduce it).