[pete]

to do a oil change on USD forks requires a full strip...
But the cheap Chinese USD forks are only USD in looks..
basically the standard forks built up side down..
Bottom allen bolt.... normally that's where the rebound damping valve is.

So I would say that holds the damping rod as in normal forks...

The real different is the spring is compressed by the slider not the damping rod..
the head of the damping rod runs in side the spring.. but they do not come apart
like normal forks by un-doing the damping rod bolt....you have to unscrew the alloy casting off the bottom of the slider "shiney chrome tube"

remove the top cap.... tip them up side down and pump them a few times..