Contax yashica adapter to sony a7s

[Aanything]

I have a couple of cheap c/y -> e mount adapters that work perfectly on my nex 5r but are almost impossible to mount on other e-mount cameras (my a7s, for example): they are incredibly hard to mount and i should apply a huge force to make them snap in correct position.
Now i need a new one, so Can anyone suggest me an adapter that mounts fine on the a7 series?
Thanks.

[Lloydy]

My C/Y adapter is a Fotga and it fits perfectly on the NEX5 and A6000. But, the tolerances of the mount are very fine and the adapters are often not quality controlled to the same standards as the camera.

I've recently fitted a Fotodiox Tough E Mount to my A6000 to replace the rapidly wearing Sony mount and my Minolta adapter that fitted the A6000 with original lens mount, and the NEX5, perfectly would not fit the Fotodiox mount without quite a bit of relieving of the adapter mount lugs with a file. Every other adapter and lens fitted perfectly. There are so many manufacturers of adapters that are all producing their items at the lowest possible cost that it is impossible to expect high quality control from all of them, most will be willing to produce crap, send it to the customer, and replace or refund it if is faulty - the customer does the quality control.