close-up of a bicycle mechanic's hand using a tool for servicing a mountain bike's transmission

wrench gear mechanic repair maintenance teeth cycling fix component transmission cassette gearshift gearwheel shop work tool cogwheel diagnostic glove garage maintain group speed steel cog showing rear chain bicycle metal mechanism sprocket transportation machine derailleur alloy pinion detail close mechanic#39aph39#s hand servicing mountain bike#39aph39#s close-up inside specialized workshop perform bike