Ron Guth: 1806 Half Cents are found with two different obverses: Small 6 and Large 6. On the Small 6, the 6 of the date is completely separated from the bust; on the Large 6, the top of the 6 is embedded in the bust. The Small 6 obverse is found only with a With Stems reverse. Two die marriages comprise the Small 6 Stems; both share the same reverse die. Cohen 2 shows the 6 in line with the arc that runs along the bottom of the digits in the date. On Cohen 3 (the rarer of the two 1806 Small 6, Stems Half Cents) the 6 is higher in relation to the other digits in the date. The differences are subtle and worth confirming because of the higher rarity of Cohen 3.
Only a single Mint State example is known of the 1806 Small 6, Stems Half Cent (PCGS MS62BN). Most examples are heavily circulated, but the PCGS Condition Census does include a number of About Uncirculated examples.
Sources and/or recommended reading:
"American Half Cents, Second Edition" by Roger S. Cohen, Jr.