The shiney bit at the top. Properly called a 'fescalized' rod.

Your forks have a fork tube and a fork slider (the top bit and the bottom bit on conventional forks), but go by various other names just to confuse you!
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball