Hello berchiche,
to create a hexahedral mesh, try using the hexahedron(i,j,k) 3D algorithm in the create mesh menu (see below)
You must then set a 2D and 1D algorithm.
For the 2D algorithm, I advise using the quadrangle mapping and define a new hypothesis to declare what behavior you'd like to observe close to faces.
For 1D algorithm, you need to use a Wire discretisation algorithm and create a hypothesis to say how you discretize all the segments of your mesh.
I think for your geometry doing this will be enough, but I also advise to create submeshes to define a smaller number of segment for the smaller 1D elements of your mesh (if you set 50 segments on all medge, you'll have way too many elements on the vertical of your disks, as the height of your disk is small in comparison to the cylinders).
Let me know if this helps;
Best,
Louis
