Ingenious dual action in small space !

A round and a flat rod, soldered together at one end,
one tightened against the other.
The nut is housed in a cover.
By turning the nut counterclockwise it presses against the housing
and presses one rod against the other.

Guitar-trussrod:
Dimensions: 460 (incl. hex nut) x 6 x 8,5 mm
Weight: ca. 170 g,

Bsss trussrod:
Dimensions: 590 (incl. hex nut) x 6 x 8,5 mm
Weight:ca. 220g 

hex nut (for 4 mm allen wrench key