Im still pretty new to bongs and dont know all of the terminology. Ive got a glass on glass bowl, wondering if theres a specific downstem i need to look for
best thing to do is take your SPOTLESSLY CLEANED bong into a head shop and just let them fit one for you.
It looks like 18.8mm > 14.5mm. (is the joint on the bowl smaller than the joint on the bong?) You could also use an 18.8mm > 18.8mm if you have another bowl with an 18.8mm joint. As for the length, measure from the tip to the top of the joint, not the lip where the bowl goes. My guess would be 4.5 inches, maybe 5.5, it's hard to tell how big the bong is from the picture. Something like this: Blaze Glass - Diffusor Adapter Downstem - 18.8mm > 14.5mm - Grasscity.com