Make holes with boolean not working - blender 2.8 I use Blender 2.8 and I made a lot of successful holes with the boolean modifier. Today is not one of those days and I don't know why.

I have a simple rectangular 2D object in which I need to cut 4 cylindrical holes.

This is what I have done:


I've used CTRL+R to make new lines on the rectangle that intersect exactly where I should place the holes 
I moved the cursor to each point and created a cylinder
CTRL+J to make a single object from the 4 cylinders
I used a boolean modifier on the rectangle and applied it to the cylinder with the operation "Difference" but I didn't get the holes


This is the Blender file: 

What have I done wrong? Is there a way to place the cylinders exactly where they should be without using CTRL+R? If I don't use CTRL+R the holes get done but then they are not in the right place...

Thank you.
Boolean modifier -> turn overlap threshold all the way down to 0. Since your objects are so small in the scene blender considered the faces as overlapping (i.e your rectangle was too thin).