It's very large - Streamlight ProTac 2.0 Rail Mount Weapon Light

This light functions as expected, and is very bright, but this review is a warning. The light is absolutely massive for a WML. It's nearly as wide as the handguard of your rifle. It's lense is 2 inches wide, with a body 6 inches long, and the mounting hardware leaves it hanging an additional half inch off the rail. It does it's job, but it looks comically large hanging off the side of a rifle. If you're looking for that "High speed, low drag" piece of kit, this isn't it.