I found this and w/ the serial number 6H312911, it's probably a Huffy, maybe a 1966.
Huffy Serial Numbers
Determining a Huffy's age requires two steps:
The last digit of the year of manufacture can be determined by the first digit of the serial number.
Then you have to look for other characteristics to determine the decade of manufacture.
Example:
Your serial number starts with "5"
Your cycle has 26 x 1.75 tires
Your cycle has a built in tank
This would be a cycle manufactured in 1965