Hello & Welcome,
Sorry I didn't see your question earlier and to hear of any issue you are having with your device.
To help you with this issue, may I ask:
1) The FULL Model Number of the devices you are working with (both the six and seven inch models?
2) What Make & Model "Friction Mount" is/was being used for the six inch device?
3) When you mention the "adaptor that works for the six inch does not fit the seven inch", what exact part of the mount system are you referring to?
NOTE: if you have a photo of the particular part that does not fit, it can be uploaded here to clarify exactly what is not working.
I see it has been a few days and I just wanted to follow up to see if you have any more questions concerning this issue or if the issue was resolved?
I look forward to any further questions or results that you may have.
Thanks, ***** *****--. .-(im)