CREATE TABLE table_67205 ("Year" FLOAT, "Denomination" TEXT, "Reverse" TEXT, "Weight" TEXT, "Diameter" TEXT, "Fineness" TEXT, "Series" TEXT)

What's the diameter of the 2006 equestrian Reverse?
SELECT "Diameter" FROM table_67205 WHERE "Year" = '2006' AND "Reverse" = 'equestrian'
SELECT "Diameter" FROM "table_67205" WHERE "Reverse" = 'equestrian' AND "Year" = '2006'