This thingy is a fuse holder for car fuse (regular type). and connector protector to prevent shorts. With the connector, I am using this thingy to make it a inline fuse holder.
The connector i am using is solderless terminal disconnector,16-14AWG

I was going to design a piece to cover the fuse too, but ended up only design the disconnector cover(since that is the only area exposing metal)

Made using Sketchup