I am not familiar with the term "one word bridge". The single-word switch indicator was introduced in order to allow one narrative (UEB) word to come between technical material without having to terminate Nemeth Code.
For example, in "If x > y and y > z, is x > z?" the single-word switch indicator is used for the words "and" and "is". The Nemeth Code terminator is placed before the closing punctuation. I'm having trouble with the braille font, but here is the transcription in ascii:
,IF _% X .1 Y ,'& Y .1 Z, ,'IS
X .1 Z _:8
If words are actually part of the math expression, they are transcribed in Nemeth Code, without contractions. For example, in "miles/hour" the slash means "per" which requires a switch to Nemeth Code. The words "miles" and "hour" are part of the fraction. (ascii again):
_% MILES_/HOUR _:
The transcriber needs to determine whether words are part of the math or simply part of the sentence structure (UEB). Sometimes this can be tricky.