Customized version of http://www.thingiverse.com/thing:1654016

Created with Customizer! http://www.thingiverse.com/apps/customizer/run?thing_id=1654016

You can buy these 4 foot long clear tubes for protecting size T12 fluorescent lamps at Home Depot for $3, they are sold near the light fixtures, not the light bulbs. They make good storage tubes if you make new caps. I made this one for storing drill bits. I wrapped a piece of paper around the tube and marked a straight line around it with a sharpie, then cut it with a sharp blade. This cap has 4 rings, the first one I made has 3 rings and works fine also. Thanks to Magonegro.

I printed with the rings down and the cap up. It bridged over the top fine with no support.

Using the following options:

InnerHoleHeight = 15
CAPOuterDiameter = 45
Rings = 4
RingHeight = 3
CAPHeight = 10
InnerMINDiameter = 39
Facets = 100
InnerHoleDiameter = 35
Fillet = 6
RingsRatio = 1
InnerMAXDiameter = 41.5