Can't insert screw by using boolean difference

Rhino Rhino for Windows
#1

Hello
I have created 3d screw model(.stl) on rhino and import them to insert into bone file(.stl).And I have the problem while I use boolean difference, the screw should be disappear and have hole in bone but it’s not! I try to use boolean union or join the component of screw but it’s failed. Help me pleaseee
Thank you very much

#2

What command did you use?

Objects in .stl format are meshes. BooleanDifference etc only work with NURBS objects. Try MeshBooleanDifference.

#3

I click on Mesh>Mesh boolean>difference
Is it because how I save screw file? I created screw and Export select > binary

#4

Another corporate version of Rhino out there.—-Mark