So mine was stripped and had to remove the rotor with the screw driver+ hammer method and remove the stripped hex bolt with pliers. What size screw fits as a replacement?

item 13 in the picture

also, is the dust cover really needed? Mine is missing.

 

Perhaps this is it:

https://rennlist.com/forums/944-turbo-and-turbo-s-forum/128705-need-size.html

My dust cap had been missing for some time. I purchased another to replace it, along with a dust seal. No ill effects running without - it is a $4 part, right?

 

perfect found that size in a screw and it worked, thanks!

 

Same thing happened to me, and my dust cover was trash so I threw it away. I went to my local hardware store and found a suitable match for the hex bolt, but you already got it!