MP5 pin
 

ok. prolly just freaking out, but what is the small pin above the trigger, in front of my fire selector, for on my M4? is it super inportant and how can i buy a replacement?

The one that goes through the entire gearbox and through the littles holes in the receiver?

thats the one

Thats the mechbox stability pin. Makes sure your gearbox stays seated properly and still within the receiver. Not entirely sure how important it is though, I don't have mine in half the time because I always forget where I've put it down :P.

Anyone have any insight as to how important it is?

It isn't THAT important, I've used/worked on M4's that dont have it, and I've never had an issue because it wasn't there.
The grip screws, rear body pin, and upper receiver keep the mechbox in place good enough without it.

Yeah thats what I always figured and thats why I never worried about it too much. If I have it on me, great it'll go in, better safe than sorry. If not, not too huge of a deal. Better off having a replacement than not though, considering they cost what, $2?

ok cool. do they have locking ones available? it seems like a pretty loose pin. for my M4! not my mp5. i dont even own an mp5 anymore. ( i know, stupid name to have if i dont)

I think it's called a "flora" pin...at least that's what I call it.

Try Airsoftparts.ca...Jugglez usually has some on hand.

lol he does, thanks man. woops, not paying 10 dollars shipping for a 5 dollar part. and xt's site has flora pins. sweet. i'll pick it up their. thanks guys.

that's why you need to order loads of other stuff so that a small pin like that ends up shipping for next to nothing. :D