Are all Nerf darts the same size?

On the outside they're pretty much the same size; however, what you don't see is that the internal plastic stem on a Streamline (aka a Clip System dart) is longer than it is on an Elite (as well as Suction and Dart Tag darts). That means that the barrel post can't go as far into a Streamline dart's "hole" as it can on the other kinds of darts.

In other Words, even though they're the same size on the outside as Elite darts, the old Streamline darts will NOT work on most Elite guns (I believe they may work on Elites like the Hailfire, Stryfe and Stockade, which use flywheels to fire the darts, but will not work on the Retaliator, Rampage, Rough Cut, Strongarm, and other guns that rely on air plungers).

Elite Darts, on the other hand, *will* work on guns designed for Streamline darts.