tapped holes

Hi, novice here but getting there.. I design a simple pulley.. couple of circles with extrudes, centre and a hole.. also an imbedded washer extrude.. Part looks perfect in Onshape, exported stl good.. looks perfect on the printer preview.. But when I print it, it's a fully formed result, minus the hole and the washer…

How do you display thread lines in a part studio? I'd like dotted lines to identify this as a tapped hole, and it would be a better representation of the hole. Thanks!