YUDIbt

This is bit simple, but will be a useful tutorial for you. If you ever wanted to model a threaded bar or a rod, you might know it is not that easy as you thought. That because you cannot use most of the modelling tools available in 3D Max to do that. I Know that most of you finally selected method must be extruding a triangular shape along a spiral. But in that method, you cannot get a good mesh for the object. But the method i am going to teach you today are very easy to follow, gut giving a perfect mesh to your object.
If you need to model a thread according to standard sizes, first you need dimensions. If you don’t have them search in the internet, you could easily find them. Otherwise, you may just used your dimensions.
For my model I have selected the M12 size thread with following main dimensions.
Major Diameter – 12.00 mm (say D1)
Minor Diameter – 9.85 mm (say D2)
Pitch – 1.75 mm (say P)
Now we can start the tutorial. First go to Front viewport of the 3D Max, and create Plane object (using Create > Geometry > Standard Primitives > Object Type rollout > Plane). Change the Length and the Width of the created plane to 0.875 mm and 12 mm. If you are using different sizes, use your P/2 and D1 for Length and Width. Change the Length Segs and Width segs to 2.

Then turn on Snap, and place left-bottom corner of the plane exactly on the origin (o, o, o) using “Move Transform Type-in” you get when right-click on “Select and Move” toggle.

After that, right click on the create plane and converted to an Editable Poly. Go to Vertex sub-object level, select the mid column of the vertices and change the X position of the selected vertices to 9.85mm (the value you taken as D2). Then select the middle vertex row and drag it near to the bottom vertex line. Now you should have something like below.

Now, go back to parent level (exit from the Vertex Sub-Object level), make a duplicate of the plane and place on top of the first plane as you can see below.

Now you having the guidelines required sketch. Go to Create > Shapes, select Line as the Object Type and draw the following sketch (follow the arrows if you can’t see the sketch clearly). Make sure to turn on Snap before you sketch it.

Once you have created the sketch, you do not need the two planes anymore. You can either delete it or hide it. Then again go to Front Viewport, and duplicate the sketch for about 20-30 times, by positioning the bottom vertex of the new sketch on the top vertex to get a continuous line like below.

Now, select the bottom-most line, and attach all the remaining lines to it by using the “Attach” button under Geometry rollout in the Modify tab (or use “Attach Mult.” Button Just below the “Attach” button to select rest of the lines from the list).
Go to Vertex Sub-objective level, press Ctrl+A to select all the vertices, and press “Weld” button below “End Point Auto-Welding” under the Geometry rollout, to connect the copied lines to gether. Start from zero and increase the amount step-by-step, until the vertices get welded. But make sure you haven’t missed any want vertex.
Go to parent level and apply “Extrude” modifier from Modifier list. Increase the Amount to 34.3219 mm (use (D1+D2)/2 x π if you used different dimensions), and let the number of Segments to remain at 1. If you worked correctly, now you are having something like below.

Select and right-click on it and select “Convert to Editable Poly”. Go to Vertex Sub-object level, and select all the vertices in one side of the object (say left).

Move the selected vertices up-wars or down-words along the Z axis to an amount equal to the pitch you have selected (mine is 1.75 mm). Take the help of “Offset:World” of “Move Transform Type-In” (right-click on “Select and Move” Toggle) to move the vertices to exact amount you need.

Then go to Edge Sub-object level of the object and select all the longer edges which connect left and right vertex lines (all the edges except zigzag lines). By keeping the selection, press the small “Settings” button, just in front of the “Connect” button under the “Edit Edges” rollout. Apply “Connect Edges” with 32 or 64 Segments as required.

Now you should get something like below.

Go back to parent level of the object and apply “Bend” modifier from Modifier list. Set the angle to 360 (or -360) digress and set the bend axis to Z.

If you have done everything correctly, you should get something like below as the result.

Go back to the viewport, right-click on the viewport and convert the model to an Editable Poly. Go to Vertex Sub-object level, and select the vertices which were coincide after applying Bend from the top viewport (see figure below).

Press the small “Settings” button in front of the “Weld” button (under “Edit Vertices” rollout). It will open “Weld Vertices”. Start the “Weld Threshold” from zero and increase little-by-little until you connected the vertex line without collapsing the model.
If you want to have a cut-ends from both ends, go to Top viewport and draw a Plane object covering the area of the screw (see figure below).

Then go to Front or Left viewport and set the elevation (by moving along the Z axis) of the plane to go through the screw. Take a copy of the plane and place it in another elevation across the screw.

Select one plane, convert it to a Editable Poly, and attach the other plane to it. Then select the screw object, go to Create > Geometry > Compound Objects > Boolean. Go to Parameters rollout and select Cut -> Refine as the Operation. Then click on “Pick Operand B” button under “Pick Boolean” rollout and select the planes. Then the two planes will disappear, but it cuts a line at the places where the planes were. Convert the object again into a Editable Poly. Go to Polygon Sub-object level and select and delete all the polygons outside the newly cut lines.

As the final step, go to “Border” sub-object level of the object, select the two open borders at the top and the bottom an press “Cap” button under “Edit Borers” rollout. This will be your final result.

This is how it is looks like when rendered.