Body Glove , Tel. O'Neill , Tel. If it doesn't seal correctly water will leak in while you're diving. The simple test is to lightly place the mask on your face without using the strap, inhale slightly through your nose. If the mask stays in place with the slight amount of suction, it is a good fit.
Dive fins are much larger than regular swim fins.
This is because they are a divers means of propulsion. There are two styles of fins, full heel and a heel-strap fin. The full heel is usually used for warm water and doesn't require a dive boot. These are not widely used by divers. A heel-strap fin does require a dive boot.