What is the main ingredient in a Screwdriver?

The main ingredient in a Screwdriver cocktail is vodka. This classic mixed drink is known for its simplicity and refreshing taste, with vodka serving as the base spirit that combines seamlessly with orange juice for a light and citrusy flavor. The choice of vodka is significant because it is a neutral spirit that does not overpower the sweetness of the orange juice, allowing for a balanced and enjoyable drink.

The other ingredients listed are not used in a traditional Screwdriver cocktail. Rum and gin have distinct flavors that would alter the drink's profile significantly, while peach schnapps is a fruit liqueur that would add additional sweetness and flavor that is not characteristic of a classic Screwdriver. Thus, vodka is the correct and essential ingredient that defines this popular cocktail.