For the bridge of the guitar, use yet another box with 3 Length Segs and 2 Width Segs. Convert it to an editable poly and do minor adjustments of its vertices to get the desired shape.
For the strings we'll use simple one-segment lines, but for better positioning we'll use some helping artifacts. In this case, I splitted one of the bridge's polygons in six by connecting two edges.
On the other side (near the headstock) I have added a box with 6 segments which will be deleted later. Six lines connecting the centers of each pair of polygons will be our guitar's strings. The only thing we need to do is to make them renderable and set a thickness for each one. Now go ahead develop your simple guitar by adding even more details.
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