do screw measurements ned to be accurate to the 10th or 100th of a mm?

I am practicing my iphone repair skills on a 5s locked to a crappy foreign carrier cheap off ebay. I took the screws out, and some of them fell away, so I ordered another packet of screws. But I need two 1.7 millimeter screws in the display connector shield, and none of them exactly match that measurement. Since these are 3rd party screws, I don't know if they're milled wrong, or if all screws are maybe a few hundredths of a millimeter off. If that's the case, how much of a .001th millimeter deficit or excess would be considered the threshold of acceptability?