4MOST, the 4m Multi Object Spectroscopic Telescope, is an upcoming optical, fibre-fed, MOS facility for the VISTA telescope at ESO's Paranal Observatory in Chile. Its main science drivers are in the fields of galactic archeology, highenergy physics, galaxy evolution and cosmology. The preliminary design of 4MOST features 2436 fibres split into lowresolution (1624 fibres, 370-950 nm, R < 4000) and high-resolution spectrographs (812 fibres, three arms, ~44-69 nm coverage each, R < 18000) with a fibre positioner and covering an hexagonal field of view of ~4.1 deg2. The 4MOST consortium consists of several institutes in Europe and Australia under leadership of the Leibniz-Institut fur Astrophysik Potsdam (AIP). 4MOST is currently in its Final Design Phase with an expected start of science operations in 2022. In this paper, the final optomechanical design and performances of 4MOST Low Resolution Spectrograph will be presented. It has been designed by CRAL for 4MOST FDR held in May, 2018. Special emphasis will be put on the technical requirements of individual optics and the mechanical design with its associated FEA.
