Slice the pickling cucumbers lengthwise into quarters.
Divide the sliced pickles into the jars.
Divide the garlic pieces, mustard seeds, peppercorns, fresh dill, and red pepper flakes (optional) into the jars.
In a 2-quart saucepan, over medium heat, add the water, vinegar, sugar, and salt. Stir until dissolved.
Carefully and if necessary, transfer the heated vinegar solution into a heatproof and pourable vessel.
Pour the solution over the pickles to completely cover them, leaving room at the top of the jar.
Let pickles cool to room temperature and then transfer jars to the refrigerator. Let pickles marinate for optimally 4-5 days.
Pickles will keep for up to four weeks in the refrigerator.