Gordon Wrubel: Liberty $20. gold pieces of 1873 were minted with both "Open 3" and "Closed 3". For the Philadelphia Mint issues the Open 3 is common and the Closed 3 is scarce. But how can one tell the difference? Look at the larger ball at the lower curve of the 3. The diameter of the ball is about the same size as the opening and would just pass through it. On the closed 3, the lower ball would not pass through the constricted opening. As a group, Type II Liberty $20s(1866-1876) are rather hard to find in Mint condition. But if you are for looking for that special coin for your type set, the condition census above shows that the 1873, Open 3 is one of your most likely candidates.
David Akers (1975/88): The 1873 Open 3 is the most common Type II Double Eagle and the commonest date of this denomination prior to the mid-1890'S. It is readily available in all grades from VF to choice uncirculated and a large number of mint state pieces are known. Because of their size and weight and the way they were stored and handled over the years, almost all Double Eagles have a fair number of bagmarks and, for this reason, gem quality (65 or better) examples of this issue are very scarce.