Earlier generations of primos Trigger Sticks had a 3/8"-16 male threaded screw-on their head and are directly compatible with the Spartan Davros.
The latest 'Primos Trigger Sticks' (Gen 3) has been designed with a mounting plate that is also suitable for mounting optics and other accessories. The plate now has a 1/4"-20 x 20mm male threaded screw.
To enable direct attachment of the 'Spartan Davros' head to this 'Primos' mounting plate, it would be necessary to obtain a suitable 1/4" Female to 3/8" Male bush. The good news is that we supply one of these with each Davros.
These are commonly used in the photographic industry and would also available from good camera shops or online retailers. We would recommend that a machined stainless steel version, as these will prove more reliable in the long run.