This is a completely customizable, higly refined, fully parametric keycap generator for spacebars made in Fusion 360. You can easily customize the geometry by changing just a couple numbers in the parametrs.
You will need Fusion 360 to customize (free software) but there are many STL files included as well including widths of 6.25U, 6.5U, 7U and Corsair 6.5U versions.
This is based on the SA profile created by signature plastics. This profile is sculpted meaning that each of the 4 keyboard rows have different angles and heights. This design builds on that and adds Row 0 and Row 5 which continue the curvature.
There are 4 parameters representing row 1-4. Just set a value of 1 for whichever row you would like to make a keycap for, and make sure to set a value of 0 for all of the other ones. This will automatically modify the angle, concave and height of the keycap for that row. That easy! Row 3 is the default for spacebars but I like to use Row 2 shape since it curves towards you, giving a nice smooth edge for your thumbs.
Instructions: