You have a very nice car there. Great that you have saved it. Unless your 39 Mercury is a very early production model, these are the two Hubcaps that you should look for. The one on the left is the regular issue, while the one on the right is the Accessory Full Stainless Steel one. You will notice that the outer diameter is larger on the accessory hubcap than the standard one, however, the inside mounting rings are the same.