Gil: The JK riser is a slightly indexed low-wrist grip. It's deeper in the throat back to belly than the standard riser. Or stated another way, the index is half as deep with the JK riser as it is on the standard riser. Also, the heel of the grip is taken down 3/8 inches from the standard riser, plus or minus a little, and worked to meet the thicker throat.
This particular grip came about last year when I asked Larry at A&H if he would just rough out a riser for me and let me finish it myself to what I considered a low wrist. Didn't want to do that, of course. After all, A&H does have quality control and its reputation to look after. However, Larry sent me a milled-out test riser and told me to have at it with file and bondo. He said if he liked the prototype, he would put it into production. The result is the JK low-wrist riser. Larry prefaced it with my initials in recognition of my contribution to the design. Now that's taking customer participation and satisfaction to the highest level.