The precision made Kingpin Bushings locate the Kingpin in a wear-free position between the hanger & Baseplate.
2.5mm is the standard size used in Trampa Spring Trucks.
The Kingpin bushings are a small item & are subjected to a lot of forces and through normal/regular use they will ultimately need replacing over time. Depending on what surface you are riding on will depend on how long these bushings will last you. So to make sure your trucks are always performing at their best inspect these Bushings regularly (preferably before riding) & in particular replace any that are showing signs of wear & from time to time replace them anyway...
The difference between the four bushings is the thickness of the base. The different base sizes are 1mm, 1.5mm, 2mm and 2.5mm. 2.5mm is the standard size we work to. As all trucks have 4 bushings this .5mm difference in each of the bushing bases allows us to bridge a maximum distance of 2mm (4x.05mm=2m) resolving any foreseeable problems.