The GPM MAKX187DP rear shock absorber shaft core kit is engineered for hobbyists seeking an upgrade in structural strength. Machined materials include 4140 carbon steel for the shaft and aluminum 6061-T6 for supporting components, increasing the shaft diameter from 5.0mm to 6.0mm to reduce bending under load. The design is compatible with both GPM and original shock assemblies and incorporates an improved oil seal geometry to minimise leakage and preserve consistent damper response.