Alan in Little Washington (NC)
Sorry, I didn't see this sooner.
I haven't used my jig lately either and I find at my advanced age, I can't remember stuff as well, however I do have a production and a few prototype IBOXes laying around the shop that I can examine and measure to refresh my memory. Plus I can give you a few ideas how to extend the capabilities of the IBOX.
First, the width of the fingers is limited to just a tad over 3/4" (not quite 1"?) It was done that way for two reasons- (1) most stacked dado blades and many TS arbors are limited to 3/4" wide and (2) attempting to make a 3/4"+ deep, through cut with a large straight or even spiral router bit can be a bit "interesting" to say the least! That being said, I made a minor modification to one of the prototypes and slowly, very carefully, and extremely nervously successfully used the IBOX to cut 1-1/8" wide fingers in poplar on a router table with a large rabbeting bit with bearing removed!
Finger length/socket depth is limited by the adjustable stock ledges, height of the fence cut-out to 1." I just confirmed that by measuring my production IBOX. Also, a small diameter dado blade which can't be raised sufficiently may also limit finger length. That being said (again), it is a simple matter to modify the IBOX to cut longer fingers (>1")- just increase the height of the blade cutout- file it or slowly and carefully nibble it higher using the saw blade. If you have a small diameter dado blade, it may be possible to remove the adjustable stock ledges to get an extra bit of height. The problem with this technique is that without the stock ledges it may be hard to position narrow stock perfectly vertical and the stock may be inadequately supported at some point along the joint. Use a square to help position the stock and clamp it securely!
Disclaimer- I am not an official representative of INCRA, so I am speaking for myself. You should always follow the manufacturer's operating and safety instructions and should never modify tools or machinery.
I still love my IBOX! (my pitch)- Over the years, I went through all the various types of DIY box joint jigs- single size, replaceable pins, screw advance, etc. etc. While I could get most of them to work at least once, repeatability from session to session was never guaranteed. Part of the problem was trying to set the dado to the exact thickness. That started my successful quest for something better. The beauty of the IBOX is that it doesn't care what your dado is set to- it can be a perfect 1/4" or .2387" or .2459", it just doesn't matter because you set the IBOX to kerf made by the blade, whatever that may be, with direct transfer. One issue- if calibrated and set "perfectly" the IBOX is likely to make a joint that is a tad too snug- no room for expansion or glue. Or if you aren't careful, the joint may be too loose. But all can be fixed with a touch of micro! Once you are comfortable and repeatable setting the IBOX pins to the kerf, you may find that each time you set it if you automatically add just a tad of micro (+/- .003", etc.) you will get a perfect joint and don't need a test cut. If you don't use it enough then usually just one test cut is all that is required.
I hope this novel helps.