E11 part from a Doopy Doo Hasbro kit

[JOker]

Just check which version of the E-11 you're building, which greeblies they have on them changes in each movie. Crypto is right, it goes on top of the mag housing, just make sure you face it the right way if you're going to use it, I have reference pics both with and without wires leading out of them, so I guess it's your call if you want them or not for that little extra....