I don't know where it came from. It certainly did not come from the size of rod you get get away with when it came to beating your spouse...

>John,
>
>>This, like the rule of thumb origin (that you could beat your wife with a rod, so long as it was no more thicker than your thumb) - is yet another urban myth that folks assume to be true...but in reality - is not.
>>
>I have wondered from time to time where that came from. Thanks.