126.320 MHz is not an aeronautical communications frequency, neither in 25kHz spacing nor in 8.33 kHz.
For 25kHz spacing (the legacy standard), when speaking the frequencies over the radio, you only should say maximum two decimal numbers, and actually old radios will only display two decimals, as the third one is implicit.
E.g., for the four available frequencies in the 126.3xx MHz with 25 kHz spacing:
Actual frequency -> Spoken over the radio
126.300 -> 126.3 (one two six decimal three)
126.325 -> 126.32 (one two six decimal three two)
126.350 -> 126.