The circuit board.
4051, 74HCT 4051 (Mouser)
74HCT4051, an 8-to-1 analog mux. This multiplexer is the magic behind the Analog Input Shield, allowing you to connect 8 analog inputs into a single analog pin. 74HCT4051 Datasheet. (6×)
IC Socket (Mouser)
16-pin IC sockets. Solder these onto the board to avoid cooking your 4051s when installing them. (6×)
Header Pins (Mouser)
Header pins; these connect the shield to the Arduino. (24 pins, 2×6, 2×8)
Reset switch (Mouser)
This is the reset switch, which you can optionally wire in.