How tight do you tighten a flash on a bridle?

When tightening a flash on a bridle, it should be snug enough to keep the horse's mouth closed without causing discomfort or restricting movement. You should be able to fit one or two fingers between the flash and the horse's nose. It's important to check for any signs of rubbing or irritation after riding, adjusting as necessary for the horse's comfort. Always prioritize the horse's well-being over a strict measurement.