The GRAvimeter for small Solar System bodies (GRASS) is a novel spring-based gravimeter for the application in extremely low-gravity environments on small bodies in our Solar System. It is one of the Juventas CubeSat payloads as part of the ESA Hera mission to measure the surface gravity on the asteroid moon Dimorphos. The GRASS gravimeter was successfully launched on-board Hera on 7 October 2024. Key element of this instrument is the gravimeter spring, a cantilever-type bending spring, allowing for measurements at arbitrary instrument orientation. This paper presents the design, manufacturing, and integration of the developed sensing element assembly. The spring design can serve as a future reference for data analysis of the gravimeter data obtained in-situ on extraterrestrial surfaces. The manufacturing process is detailed, including the raw material, laser cutting, heat treatment, and gold sputtering. The step-by-step assembly describes the integration of the spring assembly which includes the clamping of the spring and the tip mass, added to the spring to realise larger deflections and henceforth increase the sensitivity of the instrument for the small body gravity environment.