Truss rod with a hex nut that is two way adjustable for optimum setting of your neck.
These truss rods are 4.1mm wide and the spoke wheel has a diameter of 19mm. The spoke wheel can be seperated for easy instalment. You could glue it with a drop of thick CA glue afterwards.

Dimensions technical drawing (last picture):
A = 420 mm
B = 372 mm
C = 19,1 mm
D = 6,4 mm
E = 9,2 mm