As instruments are played and used, over time they wear, and also due to accidental damage they may need repair. Repairs must be done carefully to maintain the integrity and the value of the instrument. More specifically, neck grafting of a violin, viola, cello and double bass is a repair done where the neck is replaced but the scroll and peg box is kept original.
Starting round the 19th century, to improve the sound of specifically the violin, necks were made longer, and many instruments made before this time were altered by having new necks made, but the original scrolls and peg boxes were used to keep the instrument as original as possible. This was done by what is known as a neck graft. So, if you see an instrument that has had a neck graft, you can tell that it was possibly pre 19th century, but beware of fake grafts.
This repair would be similar to the violin, viola, cello and double bass. The first step would be to remove the finger board and the remove the neck from the body. Then the scroll and peg box would be cut from the original neck. A new piece of wood for the neck would selected to match the grain of the original neck as close as possible and then shaped as close as possible to the original shape, trying to keep the instrument the way it was made. The centre line of the peg box and scroll is lined up perfectly with the new neck and a joint is cut to fit the two together. The new neck is fitted to the body and before gluing, the fingerboard is fitted to allow the neck to be finally shaped. The neck is then fitted and glued, setting the angles and bridge height. The luthier will now touch up the neck to try and match the colour to make the repair as invisible as possible. If this neck graft is done well, it is often quite difficult to find.