KZ1000/900 air cleaner drain cap thread ID

In another thread Mikaw asked if someone could 3D print an air box drain cap.  

kzrider.com/forum/10-new-members/617057-...arly-40-years#861486

I've been working on drawing the cap in CAD and I'm not sure what thread type is used.  The cap has what looks like a trapezoidal thread pattern... 
Maybe something like this?

www.engineersedge.com/hardware/iso-inter...ezoidal-threads1.htm
en.wikipedia.org/wiki/Trapezoidal_thread_form

On the other side, the air box post looks totally different.  It has a rounded thread shape.  Maybe this is a common thread for plastic?  I could take a guess at the profile and give it a shot, but I'd probably have better luck if I had a clear idea of the specific thread type.

Cap:
major diameter: 14.5mm
minor diameter: 11.3mm

Post:
major diameter: 13.2mm
minor diameter: 11.2mm
thread pitch: 3mm

Anyone have any suggestions?

 

Does anyone know why this cap even exists?  It seems it does nothing.  The caps is labeled as "CAP,DRAIN" in the parts diagram.  This suggests that the two posts on the bottom of the air box, with holes in them, are intended to act as drains.  These caps go on the drain posts, but the caps have basically the same size hole in them as the post.  So the caps do nothing?  Why did Kawasaki make this part?

 

When the bike was new, it held a small piece of open celled foam that served as a filter for any incoming air and to keep bugs out. It tended to dry out and crumble if disturbed.
I just recently replaced it in my '791000 LTD.

wrote:

When the bike was new, it held a small piece of open celled foam that served as a filter for any incoming air and to keep bugs out. 

Cool!  I had no idea.  Do you have a picture or source for what you put in yours?

wrote:

wrote:

When the bike was new, it held a small piece of open celled foam that served as a filter for any incoming air and to keep bugs out. 

Cool!  I had no idea.  Do you have a picture or source for what you put in yours?

No, sorry. I think I just cut out a piece of foam I had laying around and pressed it down into the "nut". I never ride in the rain so I'm not worried about the air box holding water and I just wanted to keep the wasps from plugging them with mud. I think plugging them with a piece of rubber or anything solid wouldn't be of any harm because the boxes are not sealed that tight anyways.