A brake booster (10) comprising a housing (12); a diaphragm (16,18) mounted within the housing to define front and rear chambers (30-36) within the housing; and a cylindrical component (38) mounted within the housing and having an end (42) which passes through a sealing aperture (40) during installation within the housing to make a seal with the cylindrical component; wherein the cylindrical component has a plurality of fingers (46) extending away the said end, the fingers being circumferentially spaced apart around the end, and the outer surface (48) of each finger being chamfered such that the free ends (50) of each finger lie on a circle having an outer diameter (D1) which is less than the inner diameter (D2) of the sealing aperture prior to installation. Easier installation of the cylindrical component during booster assembly, especially where blind installation is required.