A downstem typically has two joints:

1. Male Joint: This is the upper joint of the downstem that inserts into the base of the water pipe (bong). The male joint is usually convex and can be straight, tapered, or angled to fit into the female joint of the bong's body.

2. Female Joint: This is the lower joint of the downstem that connects to the part with the bowl. The female joint is concave and is typically part of the bowl that receives the inserted male joint.
   Using an adapter as an example: 
   

The design of male and female joints ensures that the downstem can be properly connected to the bong and the bowl, forming a sealed system that allows the smoke to be filtered through water before being inhaled. It is important to choose a downstem that matches the size and joint type of your bong. Star is various sizes and joint angles available. 

How to purchase a suitable replacement downstem?

1. Downstem Length: The length of your downstem should be measured from the tip of the downstem to the end of the ground joint. To measure your pipe, we recommend inserting a pencil into the joint. Push it as far down as you would like your downstem to fit. See the diagram below.