1.   Push the bolt head in so it goes into the shaft as far as it will go

2.  Make sure the black nut is pushed down on to the castor base

3.  Push the black expander down on to the black nut

4.  Start screwing the silver nut down the bolt until it meets the expander

5.  Do not overtighten at this stage, the expander shouldn't expand at all

6.  Push the assembly up into the rail leg as far as it will go

7.  Use the allen key to tighen the bolt, you can turn it with the castor

8.  As it starts to get tight, double check it's right inside the leg tube

9.  Tighten by hand until it won't turn, do not tighten with excessive force

10. Repeat for all 4 castor wheels 

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