500 ohm, written as 501 in the code, potentiometer trimmer.

Adjusted with a screwdriver.

Resistive Material: Metal, Plastic
Body Size (Approx.): 7 x 6.5 x 4 mm / 0.28" x 0.26" x 0.16" (L*W*T)
Pin Size (Each): 5 x 0.7 mm / 0.2" x 0.03" (L*Tip Width)
Color: White, Blue, Silver Tone

A potentiometer variable resistor with 3 pins, as shown in the picture.