Thanks! I also sent an email to t-molding.com. They too suggested the 3/4" size, but recommended I trim it to fit after installing (not sure how difficult that would be - has anyone successfully trimmed t-molding once fitted?). 3/4" works out at 19mm so that's .5 mm to trim each side.
They also said they sell 11/16" (17.5mm) t-molding, but only in BLACK. If I choose black this would probably be the better option, as I reckon the .25mm gap each side would be hardly noticable, especially if I paint the edge of the wood black to match.
No mate!! Use the 3/4" ...... You'll find it's as good a fit as you'll get. Going smaller than the timber size is a bad idea. The T-Molding is there to protect the edges as well as to look good. If you go smaller it's easier to chip bits out of the timber.
Trimming T-Molding is possible... I've done it a couple of times. You get a new sharp Stanley Knife blade and let it sit flat against the surface of the cabinet, then run it down the T-Molding. It takes practice to get the technique right. so try it out on some scrap first.
That said, I think you're going to find that 3/4" T-Molding doesn't need trimming once it's in place. It will look exactly right. Like I said you're working out tolerances that are smaller than the tolerances in the timber and the T-molding. Trust me on this one 3/4" will fit fine.
Best Regards,
Julian (Fozzy The Bear)