an adaptor having ends of unequal diameters, often with internal screw threads, used to connect pipes of different sizes
3.
a layer of electrical insulation enabling a live conductor to pass through an earthed wall, etc
bushing in American English
(ˈbʊʃɪŋ)
noun
1.
a removable, cylindrical lining or sleeve used in a machine to reduce the effect of friction on moving parts, decrease the diameter of an opening, etc.