I just bought this bong and it has a diffuser with small holes. I don't want resin to get trapped inside of the holes. What size bong do I have? need to get an ash catcher for it. I put a quarter next to it
looks like an 18mm http://grasscity.com/media/catalog/product/cache/1/image/8f06e1086824bc142942bfe64f6cb67f/g/e/generic_14-18_d.stem_length_8.jpg
the diagram was very helpful. The dime sits on top of the ground joint easily so I guess it is a 18mm.
the bowl has a female 18mm joint, the down-stem which in our case, is part of the bong, has a male 18mm joint.. any attachment will need to fit onto the down-stems male 18mm joint. (they make male->female adapters and female->male adapters)
Here is rule of thumb (Pun) I learned recently, If your thumb can fit in it, it is a 18mm, if your pinky can fit in it, it is a 14mm. Awesome little trick I thought.