Nancy, I couldn't find anything on Parker wheels, but Appleton's Cyclopaedia
of Applied Mechanics, vol.11:924-925 (1895) gives a description, has figures,
and a table showing dimensions, etc. of the Leffel wheel. If you can't get a
hold of the book, I'd be happy to mail you a xerox (or fax it) if you want.n
 
Natalie Adams