This small PCB gives the trimmer resistor inside of your mod a more finished look. It fits the popular BI Technologies/ TT Electronics Model 93 1/2 inch thumb wheel potentiometer (http://www.mouser.com/ProductDetail/BI-Technologies-TT-Electronics/93PR200LF/?qs=UjOdgN%2FjCTWH6fryvuD2%2Fg%3D%3D).
This mini board is designed for 555 timer PWM builds. The PCB has 200mA, 30V surface mounted Schottky barrier diode installed in parallel between pins 1 and 3 to take the place of the 2 axial glass 1N914 diodes commonly used with PWM builds. If you building your PWM mod with a set up that already includes this SMT component (i.e. another PCB), DO NOT use this mini board.