This is an ergonomic neckblock/support for maintenance on a electric guitar. I designed it for a Fender stratocaster (2012 MIM). The neck profile fits well until the fourth fret. The guitar will lay with a flat angle on a table with that setting. The neck rest can also be used higher up the neck, though.
I really recommend to pad the contact surface (with the guitar) with some self adhesive felt or a comparable material to avoid scratches on the guitar neck.

The bottom is slightly curved so that it rocks with the angle of the guitar (pun intended).

Print in PLA with 15% infill.
Nozzle diameter: 0.6mm 
Print upside down. Use a raft for good bed adhesion.
Depending on your printer, you might want to add support for the arch on the built plate only.

A STEP file is included. But, feel free to modify the design to your needs in Onshape.