Variable resistor, 20 ohm, 3 W

To make the variable resistor unit you need 
 
Variable resistor, 20Ω, 3W (Maplin FX40T) 
Socket, 4 mm, white (JPR 705-210) 
ABS knob, white (Maplin NC63T) 
Plastic downpipe, piece of square section, sawn in half (DIY store) 
 
Construct the unit as shown in the diagram. 

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