The linkage is made up of two 1/4" Unbrako Shoulder Bolts that fit through the linkage from the inside then through two 1/4" Rose Joints for low friction and secured in place with Nyloc nuts.
The Rose Joints have threaded shafts, 1 Right hand, the other with Left hand thread connected with an aluminium shaft and lock nuts.
The opposing threads make it easy to adjust the linkage to the correct length by just turning the shaft.