Excluding abbreviations, proper nouns and affixes, I answer the question for monograms to tetragrams
Each day at breakfast Bel gives us our orders: retracing her chalk tetragrams
(and the Devil knows their purpose), and scraping the rust off these iron coffins she cherishes, their insides fitted out with sharp nails, and swabbing down the timbers of the ship, those huge, hot decks.
When in April 1969 I acquired from Ed Gilbert of Bell Labs a computer-generated list of all tetragrams
known to be in Webster's Second Edition, she quickly discovered that there were at least four words in Webster's with three consecutive identical letters: -OSSSH-, -ESSSH-, -ALLLE-, -CEEER-.
OAP can be preceded by CDEFRS or T, or followed by BEFILMOPRSTW or Y, all forming legal tetragrams
in Webster's 2nd.
Most of the quiz names aren't particularly relevant to the tetragrams
Luckily these are the very ones most apt and most ept to track down some obscure listing of their tetragrams
for themselves, except DmBo (and I bet he's still playing with words in the afterlife).
There are 24 vowel tetragrams
beginning with each of the 5 vowels, excluding tetragrams
with a repeated vowel.
In "Vowel Tetragrams
Revisited" in Nov 2003, Susan Thorpe inadvertently doubled an example for OOUO and UOUO, but omitted OOUUJ and UOUU.
Jeff Grant comments on "Vowel Tetragrams
Revisited" as follows: "Concerning the Angolan place-name with 9 consecutive vowels, I discovered CAUAIAUAIA while browsing the OSNG for Angola back in 1985, and advised the Guinness Book of Records (it is listed in the 1987 edition) and of course Word Ways (Feb 1986 Colloquy).
Runs of 4 vowels This subject was treated in detail in Susan Thorpe's Vowel Tetragrams
by Darryl Francis (74140) is, to date, the only article which directly searches for VTWs.
WW74140 Vowel Tetragrams
by Darryl Francis includes several vowel-rich 8-letter words.