In 1806, engravers at the Philadelphia mint used two different "6" punches when creating the dates on Half Eagles. On one version, the top of the 6 ends in a point; on the other, the 6 ends with a ball instead of a point. This second version is known alternatively as a Knob 6 or a Round 6 (PCGS's preferred nomenclature).
Only one die variety was made with the Round 6, this being BD-6 (Breen 5-E). This is a relatively common variety and hundreds (perhaps over a thousand) have survived to the present day. At least two hundred have survived in Mint State and these are usually found in MS62 or MS63. In MS64, this variety becomes quite scarce. In MS65, the 1806 $5 Round 6, 7x6 Stars is a great rarity, with only three known -- all of which has made their own individual appearance on the market since 2010. The record price for this variety is $126,500 for a PCGS MS65.
David Akers: This is at least as common as any other date of this type and in all probability is more available in a wider range of grades than any other Half Eagle prior to 1807. Gem condition coins are encountered with some regularity.
Quality Sales Corporation (Abner Kreisberg and Jerry Cohen) 9/1973:1159 - Harry W. Bass, Jr. Collection - Bowers & Merena 10/1999:776 - Bowers & Merena 1/2002:675 - D. Brent Pogue Collection - Stack's/Bowers & Sotheby's 9/2015:2088, $102,812.50
Heritage 1/2010:2158, $126,500
Heritage 4/2014:5723, $70,500