My problem is similar to my boolean modifier isn't cutting into my shape properly. I am trying to insert an M3 thread into the inside wall of a cylinder. I have part A an M3 bolt from the Bolt Factory, and part B a solidified Cylinder. I think that I need a difference operation. I think that I need Part B as the target to have the Modifier, and part A the bit providing the modification required.

If I juxtapose part A and B, and have the bolt as the target, I correctly lose the bottom threads of the bolt.

But if I try to operate on the cylinder B, nothing happens.

The answer to the similar question involved a prior Mirror Modifier but this does not seem to be necessary or if so why?

I am an 80-year old git, and really struggling! I can supply my shapes, but it is pretty basic in the scheme of things.

  • $\begingroup$ pls provide blend file - thx $\endgroup$
    – Chris
    Mar 17 at 10:21
  • $\begingroup$ I suspect this may be a case of the normals on the inside surface of the cylinder facing the wrong way. Please share your current blend file via blend-exchange.com following the instructions on that page to add the link to your file. $\endgroup$
    – John Eason
    Mar 17 at 10:21
  • $\begingroup$ I used Robin's example below to help. My default set-up did not display red and blue faces. I still have the problem, wonder now if I need to reorder the modifiers, such that the cylinder is still an unfilled mesh, and the bolt a mesh, make the boolean difference and then solidify the resultant. $\endgroup$ Mar 20 at 5:48

1 Answer 1


Other answers, I'm sure, will help with your Boolean. But there's no need for a Boolean, here. If you can avoid them, (which is quite often,) do avoid them:

enter image description here

Make part B from a duplicate of part A.

  • Shift S Set The 3D cursor to selected, in Object Mode, and use it as your Transform Pivot
  • Cut off the bottom of your bolt (V at the first straight circumference, progressively selected)
  • Alt N flip its faces
  • Maybe make a bit of a countersink under linear proportional editing (SShift Z)
  • Further extrude your top surface outward (E, SShift Z..)
  • Extrude downward, F Fill the hole at the bottom, I Inset the bottom face...

Then your topology will be good, the match will be exact, (you may want tolerance, but that's another question,) everything will automatically be centered... etc. etc.

  • $\begingroup$ Thanks for the great detailed response and suggestion to avoid the boolean approach. I really appreciate the trouble you have gone to. I think $\endgroup$ Mar 18 at 2:35

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