MacBook Air mid 2013 exterior screw pentalobe size?

No, I don't think your mad, but maybe on the cheap side ;-} Sounds like these drives are not well made. The technical name for the size is P5 Pentalobe we really don't get into the dimensions of the bit.

You may want to use a pick to make sure the screw head is not filled in with junk. Also, Apple uses thread-seal, I often need to use a soldering iron to head up the screw (don't get any solder on it) to soften the thread-seal a bit to get the screw loose. The last action is a drill if the head is damaged or sheered off. Just be careful with the metal shavings!