I won't post the patent pictures ~ But here are some more possible numbers ... (All of these patents are in some way related to and predate seaninNH's original cap)
( Of course, Ed-NH should be able to resolve the first number on his cap lickity-split )
2960954 ... 1960
3005433 ... 1961
3130056 ... 1964
If you are into patents, you should find the following link both helpful and interesting. I believe it was Big Cy who posted it on another thread. It is useful in many ways and in this particular instance will give you a clue about the chronological placement of 1960s patent numbers ...
http://www.oldstuffonly.com/patent_dates.asp
1960 Patent Numbers Between 2,919,443 - 2,966,680
1961 Patent Numbers Between 2,966,681 - 3,015,102
1962 Patent Numbers Between 3,015,103 - 3,070,800
1963 Patent Numbers Between 3,070,801 - 3,116,486
1964 Patent Numbers Between 3,116,487 - 3,163,864
1965 Patent Numbers Between 3,163,865 - 3,226,728
1966 Patent Numbers Between 3,226,729 - 3,295,142
1967 Patent Numbers Between 3,295,143 - 3,360,799
1968 Patent Numbers Between 3,360,800 - 3,419,906
1969 Patent Numbers Between 3,419,907 - 3,487,469