Wash and trim radishes, then slice as desired to fit inside your jars. Add the radishes, then pour the peppercorns, mustard seed, and celery seed over the top.
In a medium pot, combine vinegar, water, sugar, and pickling salt and bring to a boil, stirring to dissolve.
Once fully dissolved, carefully pour hot brine into the jar, leaving about 1/4-inch headspace. (You might not use all of the brine.) Press a chopstick or wooden dowel against the inside of the jar to remove air bubbles. Screw on lid.
Let cool to room temperature, then store in the fridge until ready to serve. For best flavor, wait at least 24 hours before eating.
Notes
This recipe will yield approximately 1 16-ounce (pint) jar.
If water bath canning, process for 10 minutes, then remove and let rest for 24 hours before testing seal and storing in the pantry.