Very old rhyming slang for tits - has been used since the 18th Century in the UK.
"Look at the threepenny bits on that chick - they're popping out, man"

"I shot my wad all over her threepennys..."
by Real cool trader April 4, 2008
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Threepenny Bit are a traditional folk band based in Southampton. They are famous for having a drum kit made out of bits and pieces, and busking in the streets of Hampshire on a daily basis.
Did you see that band on the street in the rain today busking? That be Threepenny Bit.
by nichols31290 November 3, 2011
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