This was helpful. Get to learn more.

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The Grommet?

Microphone - Aputure V-Mic D1 Shotgun Microphone (Black)

Skeleton Case - Joyoldelf Skeleton Housing compatible with all GoPro Hero4 Hero3 Hero3+ cameras

External Mic Cable - GoPro 3.5mm Mic Adapter (I found the same thing on eBay for $6.00)

Grip - Fotodiox GoTough Grip Metal Camera Light Bracket with Action Grip for Gopro Hero2, Hero3/3+ and Hero4 Cameras and All GoPro Adapter Mounts - you can get a much less expensive grip and use with the Gopro tripod adapter Heavy Duty Photography L Bracket with 2 Standard Flash Hot Shoe Mounts - $6.95 versus $49.95 for the GoTough Grip.