Hello KC welcome to the forums. we need a bit more information. what make and model of bike? did this wheel come with it or is it a replacement or upgrade wheel? I believe the pat the arrow is pointing too is the bearinf cone and no you can't get a thinner one.
how much is it off by?
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk