Dating Your Sierra D-12 Ribbed Wall Plates:
1. Plates marked "McDonald MFG CO" with NO patent reference are early 1940s -1945
2. Plates marked "McDonald MFG CO" with "Patent Pend" or "Patent Applied for" are about
mid-1946
3. Plates marked "Patent Applied For" but WITHOUT CSA mark are from ca. Late 1946
4. Plates marked "Patent Applied For" AND WITH "CSA" mark are from Late 1946 -1948
NOTE: CSA marking ("SA" inside a "C") was inspection mark introduced in
1946
5. Plates marked "Patent Applied For" AND WITH "Pat 151,907" (often in circle) are ca. 1948
(approximate)
6. Plates marked "Pat 151,907" (No patent pend or pat applied for) are After 1948