The STL file is sized for a Ukulele. Scale to around 150% for a guitar in your slicer or printer. I suggest printing the tall version since it will all your Ukulele to sit with the strings out (looks nicer).
A very solid Ukulele/Guitar wall mount. It's simple and elegant and gets the job done very well. I have a bunch of these printed and they work great! For a guitar you may need to play with the size. I set it to 150% scale for a guitar, but you will find the best size for your 'axe'.
The problem with printing something to carry weight is that most are designed from items that were not 3D printed, so when we print them they are not as strong as plastic molds or metal molds. This is designed to have a sturdier shape so that you don't have to worry about it breaking.
Suggested outer layer thickness is 2mm with at least 25% infill.
Suggested Material: PETG or Nylon. ABS will work well too if you have a handle on the warping factor. This is meant to hold weight so PLA is probably not your best bet. Maybe PLA if it's at 100% infill?