Whisk 1 1/4 cups all-purpose flour and 12 ounces club soda; season with kosher salt. Pour vegetable oil into a large heavy pot to a depth of 2"; heat over medium-high heat until a deep-fry thermometer registers 375°. Working in batches, coat 1/2 pound trimmed green beans in batter; fry until golden, about 3 minutes per batch. Transfer to paper towels and season with salt.
