Here is the Pi 2 sitting atop a Raspberry Pi version B+. It also fits the Pi 2 and Pi 3 perfectly.

TNC-Pi 2is a special version of TNC-X designed to interface directly with the Raspberry Pi computer. It can connect to the Pi either via the Pi's serial port, or via the I2C protocol. In the latter case, a single Pi can support multiple TNC-Pi's at the same time, since each TNC-Pi can be given a unique I2C address. The firmware for TNC-Pi was based on the original TNC-X open source code by John Hansen, W2FS as modified by John Wiseman, G8BPQ to support the I2C protocol as well as the original serial port connection. The TNC-Pi 2 is designed to perfectly match the form factor of the Raspberry Pi B+, Pi2 and all Pi 3 models. All 40 header pins are communicated to the top of the TNC-Pi 2 board. The standoff has been repositioned to the bottom left corner to add greater stability.