Bring a large pot of water to a boil. Season with salt and add the beans. Cook until crisp-tender, about 2 minutes, then drain and transfer to a large bowl of ice water.
Divide the dill sprigs, garlic, dill seed, salt and crushed red pepper, if using, between 2 pint-size canning jars. Drain the beans and pat dry. Tilt one jar on its side and tightly layer half the green beans in the jar, cut side toward the bottom. Repeat with the second jar.
In a liquid measuring cup, combine the white vinegar and 1 cup water. Pour over the beans, making sure they're completely submerged. Screw on the lids and shake until the salt dissolves and the seasonings are evenly distributed. Let stand at room temperature 24 hours. Refrigerate at least 3 days before eating. (The pickles are best eaten within 1 month.)