Hello Don Lewis
If you remove the 0.015" radius created on the tip of the grooves, that will revert the geometry back to major diameter of 8.625". To remove these fillet radius, you can select all the fillet faces and click the Fill tool to remove them.
If you want to preserve the the 0.015" radius fillets, there are a couple of options that can be used.
In first option, if you want to preserve the internal angle between the inclined faces of the thread, you can first create a circle of 0.015" radius whose outer distance is located at 8.625" or 4.3125" from the center and then create tangential lines from this circle which are parallel to the inclined thread faces. See below snapshot.
In second option, if it is ok to change the internal angle between the inclined faces of the thread, you can first create a circle of 0.015" radius whose outer distance is located at 8.625" or 4.3125" from the center and then create tangential lines from this circle up to the corners of inclined thread faces. See below snapshot.
You are navigating away from the AIS Discovery experience