How to sort screws without reference

Hey everyone! After being helped so well on my first question here by @Rany, i felt confident this was worth a try. As i said in my first question i am building a Iphone 5S starting with only the motherboard and the home button flex. I have every part, except the earthing clip but i have ordered that, and had a pre-installed 5S back housing with small parts, a original 5S back housing with all parts,a new lcd with all parts, 2 screw sets and a set of all small parts in a 5S. The parts, and mainly the screws, i need guidance on. How do i distinguish screws from each other? Also in my test run with everything installed, except the earthing clip ;), the phone does heat up quite a lot and the screen is a bit jittery but that i think is because the connector shield isn't on properly because i cant find the screw that's supposed to go in top right. I know that its supposed to be de-magnetized but i cant find one that is :( Sorry bout the long post Thanks in advance for any insight.