The Yamaha YDS-12 dock for iPhone/ipod has an old style 30 pin apple connector. When using a 30pi to lightening adaptor, the iPhone 8 is unsupported and liable to damage of the lightening connector if bumped.
This adaptor enables a 30pin-lightening adaptor to fit inside, and provide support for the iPhone 8.
It fits in place of the stock Yamaha iPod adaptor plate.
it is a nice tight fit to ensure that the iPhone is rigidly held.