1820 Half Eagles are made up of the following Bass-Dannreuther varieties:
1820 Square Base 2, Large Letters: BD-1, BD-2, BD-3, BD-4
1820 Curved Base 2, Large Letters: BD-5, BD-7, BD-9
1820 Curved Base 2, Small Letters: BD-6, BD-8
David Akers (1975/88)
All 1820 Square Base 2 Half Eagles have Large Letters on the reverse. This variety is of approximately equal rarity to the Curved Base 2 varieties when the Large Letters and Small letters varieties are combined. (Seperately, the Large Letters and Small letters varieties of the 1820 Curved Base 2 are more rare than the 1820 Square Base 2.) It is more rare than the 1813 and more rare from a standpoint of total number of specimens known than the 1814/3 or 1818. As is the case with the 1820 Curved Base 2 varieties, the 1820 Square Base 2 Half Eagle is normally encountered in AU or better condition.