"That's another pair of sleeves" explained

I encountered the phrase in a John Dickson Carr mystery, and decided the explanation was worthy of a separate post.  Herewith an excerpt from Friends of Cama's Blog.

"That's another pair of sleeves" is a colorful expression that we use in Italian to describe something that is about a completely different thing with no connection to a previous one. 

The expression comes from the Medieval and Renaissance use of interchangeable sleeves in men's and women's dress...

The interchangeable sleeve tradition in the Renaissance was also part of the lover's cup tradition of giving an engagement token of love to one's beloved for their wedding. Interchangeable sleeves could be so valuable that they were kept in safes.

So the next time I'm tempted to say "another ballgame" or "another kettle of fish" I'll substitute this phrase.