Jon the constant is the size or width of the kerf for the blade that you are using. Yes you can buy different thickness blades for the tool being used. To get the inlay material to match you can use calipers to measure both kerf and material. You can vary inlay thickness by sanding or cutting accurately the material down to thickness needed. I explained my method a few times here but will walk this path again for you.
I cut all my segmenting on a tablesaw with various jigs. It is the most accurate and simple way to set up jigs. For knots I do not cut all the way through. I start with a larger size blank for this reason. Usually 1" is a nice round number and works well with all kits. I leave about 1/16" to 3/32" material left. I lay the blank on a flat surface so that it is in a relaxed state. I then measure the kerf and start cutting inlay material or in some cases building it to the desired thickness if using multiple layers. I always can sand if need be to get down in size. The inlay should slide in the kerf with little resistance so that it allows for glue which I like to use epoxys. I use a small clamp on ends. Now when you squeese the blank should continue to remain flat on surface which indicates it is the right thickness inlay. If it curls up it is to thin. If it bows out it is too thick. Then after dry, just clean up to square block again and rinse and repeat. after a few it is not hard to gauge what needs to be done. good luck and hope some of this helps.
Thank you so much, John! Apologies for making you repeat yourself, I just joined the forums, so haven't widely traveled the posts yet.
Interesting point about using a larger blank and not cutting all the way through. I forget what I was watching recently, about celtic knot rolling pins, and the guy experimented with different techniques, and found that not cutting all the way through made it easier to get proper results.
Also interesting about building up materials to the right thickness...I hadn't thought about that.
Excellent tips! Much appreciated! I haven't gotten into segmented stuff yet...but I've been researching a lot. Once I have some success selling the more normal single-blank pens I'm working on now, my next foray will be into segmented stuff.