It would normally be preferable to use extrude for the rib so that it is constant thickness: if you revolve the sketch, the rib will get progressively thicker towards the outer edge. This will take care of the thickness issue. (You will need draft so the part will release from the mold, but without knowing where your mold is split I can't meaningfully recommend how to handle this. The easiest way is probably to use extrude with draft, from a sketch lying on (or parallel to) the split plane for the mold.
If the (say) outer edge needs to be cylindrical, extrude the rib bigger than you need, then use a cut-revolve to "lathe turn" the edges back to the desired diameter.
If you make one rib, you can use Insert/Pattern|Mirror/Circular Pattern to create the rest.
need to add 6 ribs in the
.09 thickness? Do I need