I have created three signing keys for my Apple iOS
One for my development signing
One for Ad Hoc
and One for Distribution
When I open the signing keys in my account it shows the Development Key as the default but no other options are given to set any of the other keys as the default.
Why is only one of the keys showing the default radio button
Production signing keys can't be set as default. But in your app you can select a production signing key and it will lock the app to that key.