Nesting Ashtray 6¾" circa 1958, Ebony Cascade glaze, photos courtesy thebrassmonkeyatpeytonsplace on eBay

Notes:

1. The above information is for R-1820 as R-1820-S has not been found in a catalog and they are assumed to be the same design. An example marked R-1820 is not known.
2. The catalog lists three Nesting Ashtrays as a set:  R-1819 (8¾"), R-1820 (above), and R-1821 (4½")

Bottom reads:  ROYAL HAEGER R1820-S U.S.A.