The screwdriver can be turned while you hold the nut steady
and vice versa
End view shows the 8mm socket with the screwdriver head
The 11" long screwdriver slips out of the nut adjusting shaft
The Carbtool is for older bikes that have an adjuster screw held by a locknut. The Carbtool has an 8mm socket to tighten the locknut.
Down the centre of the tool runs a long screwdriver to hold the adjusting screw stready while you tighten the nut.
The screwdriver has a 280mm (11") shaft.
Most modern bikes don't use this as the adjusting screws are spring loaded. Check your bike before ordering.