Instructions for threaded container

put a 2mm square plane at origin

Edit mode

Loop cut in half parallel to the y axis

Delete faces and middle edge

Merge the outer edges parallel to y axis at center

Bevel those two verts to about a 45 degree angle

Still in edit mode, move the shape 20 mm in the X direction

Object mode

Generate an array set to 2

Orient the array slightly above and to the right

Generate a screw after the array

Two iterations, 128 steps

Give the screw height so that the shapes thread together

Make sure normals are proper

Give the threads some breathing room so that they print well

Copy these and hide them as a backup

Apply array then apply screw

Check normals

Separate by loose parts

Fill in missing faces

Rotate threads so they are oriented around Z

Add cylinder with ample faces, 128

Scale to fit the inner thread

Inset top and bottom face arbitrarily being sure the thread doesn’t cross to the inside

delete the top and bottom inner faces

Fill the inside 128 faces so it’s a hollow cylinder

Copy this object and scale it to fit the outer thread

Generate Boolean union inner cylinder inner thread

Generate Boolean union outer cylinder outer thread

Give the bottom cylinder a bottom by extruding the bottom ring of faces 10 mm, then again 2mm

Delete the 2mm ring of faces

Fill the inner circular faces at that bottom 2mm area

For the top cylinder, extrude the top ring 1 mm then 2 mm

Delete the 2mm ring of faces, then fill the top and bottom inner circular faces