In the 1400's a law was set forth in England that a man was allowed to beat his wife with a stick no thicker than his thumb.Hence we have 'the ruleOf thumb'
Thought rule of thumb had either to do with a "green thumb" or something to do with measurements, the length of an average thumb, maybe?
Many years ago in England , pub frequenters had a whistle baked into the rim, or handle, of their ceramic cups. When they needed a refill , they used the whistle to get some service. 'Wet your whistle' is the phrase inspired by this practice.
In English pubs, ale is ordered by pints and quarts.. So in old England , when customers got unruly, the bartender would yell at them 'Mind your pints and quarts, and settle down.' It's where we get the phrase 'mind your P's and Q's'