Exotic Diamonds what are they used for ?

I have looted 4 exotic diamonds what are they for ? they all have different names, so far they once I have looted are called

"Pistol: Trigger and Mechanism 1/1"

"Pistol: Receiver and Paintjop 1/1"

"Pistol: Sight and Rail 1/1"

"SMG: Modified mods 1/1"