soundknight21, please go on... Another post equally as long about fret shape and size. This is the one thing that really eludes and supasses my understanding... There are so many different opinions on this one and I would be very interested to hear yours.
One thing I'd add (or more of an example of what you're talking about above): I have an irregular shaped first finger on my left hand. It's slightly curved with a rather larger indentation at the joint. This gives me terrible issues with certain barre situations and I have to have extremely accurate placement to avoid loosing notes sometimes. In my case this is an important factor when considering string spacing as a tiny bit closer spacing (and perhaps even a slightly larger) changes where different parts of my finger will sit. These types of variables are why there can never be a rule of thumb that would work for everyone and at best we can come up with generalizations about what may work best.
Another thing not mentioned already is action as this effects all the other variables mentioned here.
So to sum up the posts on this page: Rule of thumb for fitting hand size to fretboard length (as well as string spacing, string tension, etc): Play as many guitars as possible with as many variations as possible to find the variation that works best for you and your particular body type and size and hand type and size, etc. and your style of playing and music you play. Perhaps the best reason why a beginner shouldn't run out and spend several thousand $ on their first guitar...
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