A potentiometer for controlling an electrical circuit, wherein the electric circuit belongs to an electrical device provided with a control panel or distribution board, comprising: - a cylindrical case having an enlarged and open upper edge portion and being adapted to be inserted inside a hole present in the panel or distribution board of the electrical device to be controlled; - means for removably anchoring said cylindrical case to the panel or board; - an electric adjustment device housed in said case and enclosing a variable resistance, said electric adjustment device comprising output terminals; - means for the electrical connection of said electrical adjustment device to the circuit to be controlled and having a terminal board provided with output terminals adapted to be electrically connected to the circuit to be controlled; - a drive shaft having a longitudinal rotation axis with a first end and a second end adapted to interact with said variable resistance to vary the instantaneous value thereof upon the rotation of said shaft; wherein said electric adjustment device comprises a box-like housing coupled to said electrical connection means and housing said variable resistance, said housing having a longitudinal passing-through hole suitable for snugly fit said second end of said shaft to bring it into contact with said variable resistance; characterized in that a knob is provided, said drive shaft being integral in rotation with said knob at its first end, said knob being partially inserted into said case to be handled from the outside and in that said electric connection means consist of an electrical conductive plate arranged longitudinally in said case and adapted to place said output terminals of said adjustment device in electrical continuity with said input terminals. - a cylindrical case having an enlarged and open upper edge portion and being adapted to be inserted inside a hole present in the panel or distribution board of the electrical device to be controlled; - means for removably anchoring said cylindrical case to the panel or board; - an electric adjustment device housed in said case and enclosing a variable resistance, said electric adjustment device comprising output terminals; - means for the electrical connection of said electrical adjustment device to the circuit to be controlled and having a terminal board provided with output terminals adapted to be electrically connected to the circuit to be controlled; - a drive shaft having a longitudinal rotation axis with a first end and a second end adapted to interact with said variable resistance to vary the instantaneous value thereof upon the rotation of said shaft; wherein said electric adjustment device comprises a box-like housing coupled to said electrical connection means and housing said variable resistance, said housing having a longitudinal passing-through hole suitable for snugly fit said second end of said shaft to bring it into contact with said variable resistance; characterized in that a knob is provided, said drive shaft being integral in rotation with said knob at its first end, said knob being partially inserted into said case to be handled from the outside and in that said electric connection means consist of an electrical conductive plate arranged longitudinally in said case and adapted to place said output terminals of said adjustment device in electrical continuity with said input terminals.