I've never liked thumb picks because by the time I got one that fit securely enough, it would squash my cuticle into the nail bed below. This design has a contoured interior that distributes the pressure evenly across the nail and the back of the thumb.
This particular version is a combination flat pick/thumb pick for those of you who (like myself) can't manage to pick 10 notes with a flat pick without the pick flying loose. I've tapered the pick thickness to make it sturdy yet with a little flexibility at the tip.
This pick prints on edge using the native orientation in the STL file. Print in PLA with 0.2mm layers and 0.4mm line width for optimal strength. The STL file has built-in support for the thumb section that peels away easily, so no additional supports are needed. Print this pretty slowly and hotter than usual to make sure the layers fuse completely. You may also want to print with a raft.
Once printed, peel away the raft and supports and then sand the tip down with 320 grit sandpaper until it is completely smooth.
Note: if you scale this pick up or down to fir your thumb, you should also scale the line width proportionally.