Its two black plastic plates sandwiched together with ball-bearings and grease in the middle.
Mine fell apart when I originally built it, so I threw them out. But now I get a squealing when turning the steering at low speed when hot.
No. 11 on the attached diagram.

I think they should go back in, but it will raise the ride height and mean I'll be running the front dampers on the bottom of the spring perch adjusters. i.e. Might compromise how low I can get the front.
Any advice welcome?
GarryG