Bike  is all dressed up and no where to go because I found this and afraid to drive it until I find our where it came from.
I found it laying on the driveway close to the bike. Not sure if it is a random part that fell out of a box of parts or it fell off of the bike.
It looks familiar but I don't know exactly where I saw it before.  Its hollow and treaded and a little over half an inch long.

I looked at that for 10 minutes. Does not ring a bell, but, I did notice all the scratches in what looks like a copper washer as if it has sat in the driveway for awhile and got run over a few times.  I'll go look under my bike and see if I got anything that looks like that. I'll get back to you on Thursday. Check the thread size and see if it's metric, any car parts store can do it, or, home depot has loose fasteners in bins.

Looks too small to be a Sump plug but that is what it resembles. What diameter is the thread? I  assume it's a Hex head on it?

Is it the cap that goes on the Cam Chain tensioner?

Ride safe, Ted

There are a bunch of a-holes on the Facebook forum. Right away I said that it is not the oil drain plug because I could see mine and there was no oil slick under the bike. But they kept insisting that I had burned up my motor because I ran it dry of oil.  I've been under the bike for quite a while and there are no missing plugs and there is no dripping oil.

Connie Rider wins the contest. It is the cap the hold the tension spring on the cam chain tensioner.
Thank you very much. I should have come here first instead of arguing with those guys on Facebook.

Good spot Ted 
That hollow center should have clued me in.

As for the Facebook group, if that is the COG Facebook group then your assessment of many of them is exactly why I am no longer in that group.

Either that or you are just being silly..

Found the reason it came off.  The threads are stripped. You can hand tighten it but you cant use any torque or it will just spin. I guess its been like that for a long time. Finally vibrated itself out.
Ordered a replacement from ebay.

If the cap is off the bike, the spring and plunger are also gone..
Hopefully you ordered the entire tensioner?

Ride safe., Ted

PS: I'm still a COGger and participate in the COG Forum and Facebook. (ie; We're not all ass____s) 

Yes I ordered the entire tensioner.

The spring and the little pushrod were still in the tensioner body....just lost his hat...lol

I was wondering about that...

PS: I'm still a COGger and participate in the COG Forum and Facebook. (ie; We're not all ass____s) 

Ted, we love you and forgive you.   

Most of the people on the COG forum & FB Group are not-a-holes.
I've met some awesome people through COG.
I would still be on the FB Group if they hadn't handed control of it to certain people.
I would still be on the COG Forum if they hadn't decided to kick non-paying people off it.

Gpineau, did you order a replacement Kawasaki tensioner or a manual one?
I've got a manual tensioner on my project C10 and have a late model OEM one on my 89.

I ordered the Kawasaki tensioner. I don't trust myself to tension it correctly.

It was a serious question I posed on Facebook forum.  I was worried about my bike and they (many) kept insisting that it was the oil drain plug although I verified it was not.
So I guess not all of them are a-holes but a certain percentage come close.  Sorry if you were offended.

Well I waited a week for the part and it is the wrong one. It is shorter than the original and does not have the push rod and spring. Instead it has a screw inside that you must turn to relieve tension while installing but I'm not going to use it. I will order another one and make due with the old one with the stripped out threads. I drilled and tapped a hole in the side of the barrel so I can use a set screw to hold it until a new one arrives.

Good enough for a temporary fix.

Well I waited a week for the part and it is the wrong one. It is shorter than the original and does not have the push rod and spring. Instead it has a screw inside that you must turn to relieve tension while installing but I'm not going to use it. I will order another one and make due with the old one with the stripped out threads. I drilled and tapped a hole in the side of the barrel so I can use a set screw to hold it until a new one arrives.

Good enough for a temporary fix.

The one with the screw slot that you turn to pull the tensioner in with is the 86-93 tensioner and is crap.
What you need is the later model tensioner. Order one for a 98 or later and you'll be fine.
If buying used, make certain it's the later model like this one https://www.ebay.com/itm/252723589374

you are right it is crap. It is barely long enough to reach the chain guide and it does not feel like it has much tension at all. I have another one on the way. Right one this time.  Meanwhile getting by with my cute fix.