The web site
Innovations and Insights TipNut offers this clever way to remember which months have 31 days and which have 30:
Count the months on your knuckles and the grooves between your knuckles. Leave out your thumb knuckle. Every month that lands on a knuckle is 31 days, every month that lands on a groove between knuckles is 30 days (or 28 for February).
You know what? It's silly, but it works. Finally, a more peaceful use for knuckles.