Printed in 3 pieces, this will hold a iphone 7 plus (or iPhone 7 or iPhone 6) and attach to a standard screw on a tripod mount. I re-mixed the threads, and copied the bolt, found at other posts. I prefer my solution since it uses a small number of components, it is very sturdy, and it supports a range of different mount configurations.

I printed this and I have used it several times without any issues.