Brain Game: Hardware Wars

I visited a local hardware store today and bough popcorn and diet soda... not typical hardware store purchases. But today's Brain Game IS about something you'd likely buy at a hardware store. Try this one on for size:

You visit a local hardware store for a particular purchase.
The clerk tells you that 6 would be $1.50
and that 12 will cost you $3, but adds that
he'd be happy to sell you 9680 for only $6.

What is it that you're buying?

See the answer here.