Just got this from Mark at Incra;
"Hi, David -
The I-Box has no problem with 7/8" thick lumber (which is the deepest cut) and cutter widths between 1/8" and 3/4" (therefore, 3/4" is the max spacing). Let me know if I can address any questions on the jig or its applications - 888.804.6272 xt 4.
Field Operations Manager
Thanks everyone for your input.