Zither tuning pins are the commonly-used pins for hammered dulcimers. Typically, you use two pins for the two strings that comprise a "course" of strings. That is, the strings are doubled, and those "wrist pins" or "hitch pins" are what the one wire that comprises the course goes around at the other end of the instrument.

That reads funny. Let's start again.

You probably would want to double the strings, which you do by putting two tuning pins in the pin-block on one side, and a single hitch-pin on the other block. Run your string from one tuning pin across the bridge to the hitch pin, then back across the bridge to the second zither tuning pin. Tighten carefully till both strings in the course are at the same note. Do the same for the rest of the strings.

Then retune interminably till it settles in.

Now, for a kid's project, you may want to use single strings. In that case, put a hitch pin lined up with the first tuning pin, and a second a decent distance up the pin-block, in line with the corresponding tuning pin. Now the single string goes from one tuning pin, around the first hitch-pin, up to the second, and back across to the second tuning pin. The result is two single strings, each tuned to a different note, and separated enough to be played as separate notes. If you want the strings an inch apart, your pins will all be more or less an inch apart (allowing for the fact that the instrument is a trapezoid, and one inch in the middle, across the bridge, is really slightly more than an inch on the slanted end-blocks.

So one string can be one note (in courses) or two notes (in separate locations).

Does this help?

Bob