This small pin is using 12*3 Nd magnets with 4mm screw hole in them.

There are 2 versions. 

First must be printed with pause at layer for inserting magnet.

Second have magnet attaching pin printed separatly. Still I suggest to pause at leyer to use magnet as support.

There is also hole in the body for attaching string and fishing things out of tight places.

Print time about 15 min. I Suggest printing them in bulk.