inner

Inner Circle: 6 short vowels; symbols are all single; these vowels never end a syllable.

corners

Corners: 6 long vowels; symbols usually have ː but /eə/ also considered a long vowel in this model.

sides

Sides: 6 dipthongs; symbols have 2 elements; the sound moves from one position to the other.

long-short

Long-short vowel pairs: Each pair shares similar mouth position.

schwa

Centre: The weak vowel also known as 'schwa'; only used in unstressed syllables; the most common sound in English.

r

Optional r: The letter rusually comes after these sounds; pronounced in some accents not in others.

r

More info:
Read full infographic: The PronPack Sound Chart
Watch: video explanation

r

Sources:
Audio files from: abelard.org & Forvo.com
Original code: dodecagondiv
Original code: Sound For Mouse Hover Script