This is a Parker 51 Vacumatic Custom in Cedar Blue with 1/10 16K gold filled Blue Diamond cap date coded 1946. Usually Custom caps were 1/10 12K gold filled. Note that this pen's Blue Diamond has been repainted. Unfortunately the paint work got onto the diamond border as can be seen under a loupe, something to take note when getting a pen serviced if it needs this done. There are multiple versions of the Custom cap. This one has sets of four vertical lines separated by a plain band, probably the most common version. This 5 3/8 inch long pen has the clear plunger filler unit and sold for $15.00.