Thanks for the reply. The last picture was so poor it didn't really show the inside of the spindle but it looks like this, which made me think another tool may be necessary:
No other tool required. 10mm allen key to remove it, 10mm allen key to install it. Nice and simple.
@Brommers started
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Thanks for the reply. The last picture was so poor it didn't really show the inside of the spindle but it looks like this, which made me think another tool may be necessary: