C'mon - some of you don't know what crank dust covers actually do? For real?
A clue: they most definitely serve a purpose, depending on the type of crank/BB - for example, you don't need them on
cottered cranks.
"A dustcap may also refer, on a bicycle, to the
crankarm bolt cover. It is usually a piece of metal or plastic that, on the crankarm, is snapped or screwed into the threaded
counterbore, which houses the bolt that holds the crankarm to its axle, the
bottom bracket spindle. The dustcap serves to protect the threads (on the inside of the counterbore), which are used with a
crankarm puller to remove the crankarm from the spindle. It is also possible for the crank arm to squirm on the bottom bracket spindle, causing the crankarm nut/bolt to become loose, leading to the nut/bolt working its way out of the bottom bracket spindle. The dust cap limits the amount of dangerous loosening that can occur."
DD