Downpipe / Bowl and Stem 18.8mm joint size

Downpipe and Bowl (no extra screen nec.)for 18.8mm ground joint glass bongs. Please measure the length of the downpipe from underneath the bowl down to the end.
1. How do I measure the Length of the Downpipe correctly?

2. Please state this length of your Downpipe and Bowl in the comments field at the end of the ordering process.We'll cut your Downpipe / Bowl and Stem accordingly.