Hey there,
the object shown is a bass reflex tube. You can see this little triangular nose. I just draw two lines on the ring surface below (an arc). The endpoints are touching the tube. This result is that funny little… thingy thing. 
But what I really want is such a diamond like nose from my hand drawn sketch.
Any ideas how to manage that? 
Thanks in advance,
Frank
Here’s one way.
“Move/Rotate” - It’s that simple! Thank you Mike. 
Okay, now I have a next question. I need to rotate this thing around the tube to get 5 of these. Do I have to copy it 5 time and place it manually or is there an automatism?
Thanks,
Frank
Move/Rotate (copy) the triangle body about the center of the cylinder.
Yap, I got it in the meantime, too. Thanks Mike! 
Hint @Istvan: An option of entering a number of copies while rotating around an axis (with even spacing) would be very handy!
