What does joint size mean?

What does Joint size: 18.8mm > 14.5mm mean?

• I'm buying my first bong off soon (first paycheck with a new job this friday, 74 hours worked, so I got a little bit of spending money haha) I found a Molino I want, because it is 7mm thick, and I'm a klutz haha. I'm definatley going to get a precooler and it says Ideal downstem/ diffuser length 14 cm approx. Then joint size 18.8mm> 14.5mm. What does that mean? Do I need to buy a 18.8mm or a 14.5mm? I know what the length means, but I'm confused on the joint size. Do I buy a 18.8 or 14.5? Actually I'm a full time student and I'm now scheduled for 35 hrs a week. A junior in high school that's half way through their training as a phlebotomist, beginning college classes 15 credit hours a week 1st semester of my senior year to train as an EMT-B, with an over all GPA of 3.63. So before you begin condescending on someone try and think of what you know, or more importantly don't, about them. Also, you have no idea what I was going to use this for, tobacco or weed, as you seemed to have assumed that it was for that. So piss off.

• Answer:

  Wow thatsfuckin awesome! Will you be going to college in the near future or flipping burgers at your "NEW" job?