The Prime 5ths are the 5ths contained within the Prime Octave that use A3 and A4.  

The Lower Prime 5th is: A3/E4.
he Upper Prime 5th is: D4/A4.

The Prime 5ths can be used to determine the width of the Prime octave.
This is a new approach to determining the width for the prime octave.

Prime 4ths

We refer to the pair of 4ths contained within the prime octave that use A3 and A4 as the Prime 4ths.

The Lower Prime 4th is: A3/D4.
The Upper Prime 4th is: E4/A4.

These upper and lower prime 4ths are basically ‘resultant’ intervals when balancing the prime 5ths.   They are rarely ‘measured’ but are very handy aural checks when balancing the 5ths.