Thanks for the reply! I have a standard straight tube bong. I'm not really sure what female/male joints are but I found a picture on google to illustrate where I made the measurements.
I basically measured straight across from the beginning of the opening to the end and not the frosted circular...
I'm trying to figure what size adapter I need. I've measured the downstem straight across and got 14mm. I've also measured the hole in my bong where you insert the downstem, and got 20mm from measuring it across. Which measurement do I use? 14mm and 18mm are the options available for the adapter.