I was driving past the village of Hampsthwaite the other day, and happened to spot the six consecutive consonants in the middle. It set me wondering whether this was the most possible, and if not, which word contains the maximum number?
Archchronicler, catchphrase, eschscholtzia, latchstring, lengthsman, and postphthisic each have six consonants in a row.
HIRSCHSPRUNG'S (DISEASE) has seven consecutive consonants, as does SCHTSCHUROWSKIA. The shortest such word is TSKTSKS. All of these words can be found in major English dictionaries.
Twelfthstreet (normally two words but sometimes written as one, as in a song title; Eighthstreet is feasible by analogy), and Hirschsprung, as in Hirschsprung's disease (though this is after a Danish surname). The scientific name of the white (or Tubergen) squill is Scilla mischtschenkoana, and the transliterations of several Russian names, such as Tischtschenko, contain the same constellation of seven consonants.
Sorry if this is a tad off-center, but the longest sequence of typographic (as opposed to phonologic) consonants in a single syllable may be five, in the words strengths and lengths. (Strengths may be the one-syllable word with the largest number of [spelled] consonants: 8.)