This is a C7 version of the C9 covers http://www.thingiverse.com/thing:1637357
The shape and size has been made as close to a classic Incandescent C7 bulb as possible.
The base features a 13mm thread that will screw down over the soft plastic surrounding common LED Pixels used in Christmas lights. I have tested this on quite a few different pixels I have and it provides a secure fit that is far less likely to come off than the original push fixture.
The shell is 0.8mm thick in the design aimed at two perimeters using a 0.4mm nozzle.
Two STL's are provided, one is a classic smooth exterior and the others features random facets that give an external texture but don't really change the light too much
C7 facet... .. light facets
You could print in translucent colours for white leds
Print them slow till you are successful
Translucent ABS works really well for these. I print these exclusively sliced with S3D using 3 processes, one for the base, one for the main section and one for the top 20 layers. I print the top 20 layers at 0.1mm to ensure a nice water tight finish though 0.2mm should be fine.