MAKING SCREW & NUT THREADS SIMULTANEOUSLY:

Step 1
Create a spring: 19 loops, 12 segments, 2 sections and center in the view.

RMB>LMB: More>RMB: Spring
Tab 19 Tab 12 Tab 2 Enter
CtrlA Menu:Tools>Center>All

To open primitive option: RMB on the primitive name or LMB on the square near the primitive name.

Step 2
Deselect. To have the 2 end faces in X axis, cut the first 11 top segments.

Space E LMB: select 1 edge L
RMB>Loop Cut <—

Or select the top end face, hit '+' 11 time and dissolve.

Step 3
Scale the spring to 40% Y axis.

CtrlA RMB>LMB:Scale Axis>LMB:Y
CtrlMove to 40% in top Info line.

Step 4
Duplicate the spring X axis and move the copy to 4wu from the original.

RMB>LMB:Duplicate>X
ShiftMove to 4wu

Step 5
Deselect. Loop Cut the bottom part of the copy: keep only 4 loops.

Space E LMB: select an edge L
RMB>Loop Cut
Deselect top part Select bottom part <—

Step 6
Select the top vertex on one end face, then similar and connect.

V LMB:select vertex I C

Step 7
Deselect. Select one of the news vertical edges on end faces then select similar. Select edges loops and Loop Cut.

Space E LMB: select edge I L
RMB>Loop Cut

Step 8
Invert the proposed selection (or Select the 2 inner parts) and dissolve.

Shift Ctrl I (Mac Shift Cmd I) <—

Step 9
Select one outer edge of one spring then select similar.(See italic note below)

E LMB: select 1 edge. (See note below)I

Or jump directly to Step 11...!!

Step 10
Choose Face mode: all external faces are selected. Select one end face (e.g. yellow on the picture) and similar.

F LMB: select a face I

Step 11
Inverse the selection.(See italic note below)

Shift Ctrl I

NB: If you come from Step 8 over 9-10:
here you can simply select the 2 inner faces!...
(Thanks pp! ;)

Step 12
In Vertex Mode, connect all interior vertices.

V C

Step 13
Deselect. On the top of one spring select the 5 top faces then similar, and dissolve.

Space F I <—

Step 14
Deselect. Select the (new) top face of each spring and extrude Y axis (any positive value).

Space LMB: select 2 faces RMB>LMB:Extrude>Y
CtrlMove >0.1wu

Step 15
And make an advanced Y flatten to the top of the spring and valid.

RMB>LMB:Flatten>RMB:Y
LMB:pick the vertex on top of spring RMB:Clic

Step 16
Deselect. Move the view to see the bottom of the short spring and pick the last vertex of the external loop as 'Bounding Box' (BB).

Space MMB: move the view V
LMB:pick the vertex
Menu:Tools>Save the Bounding Box

Step 17
Deselect. On the bottom of the long spring, select the same vertex and ask to move to saved BB in Y axis.

Space LMB: pick the vertex
Menu:Tools>Move to Saved BB>Y

Step 18
Deselect. Select one bottom face, similar and extrude Y axis (any negative value).

Space LMB: select face I RMB>LMB:Extrude>Y
CtrlMove -0.1wu

Step 19
Make the same advanced flatten as in step 15 but to the bottom of the spring and valid.

RMB>LMB:Flatten>RMB:Y
LMB: Pick the vertex on bottom of spring
RMB:Clic

FINISHING THE THREADS:

Step 20
Deselect. Select one oblique edge at end of a thread, then similar and dissolve.

Space LMB:select edge I <—

Step 21
Select all bodys and clean-up.

B CtrlA RMB>Clean up.

You must have: 2 objects, 824 faces, 1662 edges, 842 vertices.

Step 22
Deselect. Select the 2 vertical edges after one end face of spring, then similar and connect.

Space LMB:select 2 edges I C

Step 23
Deselect. Select the top new vertical edge after one end face of spring, then similar and cut in 2 parts.

Space LMB:select 1 edge I 2

Step 24
Deselect. Select the vertical edge of one end face of spring, then similar and dissolve.

Space LMB:select 1 edge I <—

Step 25
Deselect. Select the 4 vertices as shown at one end face of spring, then similar and connect.

Space LMB:select 4 vertices I C

Step 26
Deselect. Select one last vertex of the external loop of spring (see picture), then similar and move to bring it closer to the body.

Space LMB:select vertex
RMB>LMB:Move>Normal
CtrlMove to -0.1wu.

Step 27
Deselect. Select one circular end face on a thread, similar and extrude Normal axis slightly.

Space LMB:select a face I
RMB>LMB:Extrude>Normal
Shift CtrlMove to 0.06wu.

Well. Now choose the Simultaneous HEADS in the menu...