Pickling Salt is a very fine grained pure food-grade salt used in pickling.
It is as fine as table salt — in fact, it is table salt, but without any additives.
Additives in table salt, such as iodine or anti-caking agents, would, if used in pickling, turn pickles brown and make the brine go cloudy. The resulting pickles would be fine to eat, but unappealing and make people think there is something wrong with them.
You could also, if you wished, use pickling salt as a table salt.
You could substitute any completely pure, additive-free sea salt – but the salt branded sea salt may be more expensive. Some brands of Kosher Salt can be substituted: either the ones that have no anti-caking agents, or if they do, if it’s sodium ferrocyanide (yellow prussiate of soda), as that won’t affect your pickling the way other agents will.
Note that if you are using a coarser salt than Pickling Salt, use 1 cup plus 2 tbsp of the coarser salt for every cup of Pickling Salt that you need if you are measuring by volume. If you are measuring by weight, in ounces or grams, just substitute weight for weight.
But economically, you’re better just getting the Pickling Salt as it is quite cheap and is sold in largish bags and boxes, which is the quantities that you’ll need in preserving, anyway.
1 cup = 7 3/4 oz = 220 grams