Also meant to say, the slot in the nut can easily be widened, if that's a problem. There's going to be a particular ratio of size to pitch within which the lowest pitch of a dulcimer will still sound good, but I've not experimented in this way with a dulcimer so I can't advise on how low won't work. Experiment - what can go wrong? Even if you try too low to work, just change the strings and higher the pitch. If you widen the slot on the nut to fit a thicker string and the pitch doesn't work, a wider slot shouldn't be a problem for a thinner string (within reason) and, if it is, there are plenty of folks who can make you a new nut. Experimentation is always worth while, even if it doesn't work: you never know what you haven't tried.