IT is my understanding that the difference between a tenor and plectrum banjo is the length of the scale. While the Guest is correct in that they are similar and both have four strings a plectrum banjo has a much longer scale. More nearly that of a five string length, about 26" is the scale to a plectrum banjo. Tenors are shorter and to add to the confusion, some tenors are 17 frets in length and some are 22 I think. Their scale lengths I don't know but I'd guess about 24" or less.

Don