Hi Kevin,

You can find details on several variations of J-tools in:

James B. Shaffer, Lee A. Rutledge, and R. Stephen Dorsey,
"Gun Tools: Their History and Identification"
Eugene, OR: Collectors' Library, 1992, ISBN 0-9631208-0-8.

(Great info on lots of different tools in this book, including Enfield combination tools.)

Geoff