Length: 16mm
Inner diameter: 9mm
Outer diameter: 16mm
I used a drop of handgrip cement to hold each collar to the underside of the top rack to help with aligning the bolts and holes.
Trunk Mounting Bracket.pdf
The OEM top rack can be used with or without the pannier racks. Use the long collars for the non-pannier rack installation.
I will measure the dimensions of my long collars in a bit, unless someone else chimes in first.
The hinges have hard stops just past 90 degrees IIRC. With the bags off the bike, I temporarily remove the cords for packing and unpacking, being careful not to stress the hard stops.