What's the deal with this post?

[Lando]

I have a Dr. Pepper keg that I picked up on CL several months ago. I went to clean and change the o-rings and noticed the beer out post wasnt screwed down. A 3/4" wrench fits the post, but no matter what I do it will not fit the thread. The threads look similar. Other keg posts fit the keg, no obvious burs are in the post. Any idea what WTF is going on with this?
Are DP kegs some strange size thread?

 

[david_42]

Do the threads look damaged?

 

[Lando]

They look OK on the post and keg.
No idea why this will not fit.

 

[david_42]

Then the most likely explanation is the person you purchased the keg from got his posts mixed up. Different manufacturers use different posts, poppets, lids and pipes. A slightly undersized post will seat in a hole, but you won't be able to get the larger post into the smaller hole. The differences are small. You'll have to locate a new post from the same manufacturer.

 

[SpanishCastleAle]

The Gas IN post should have little slots in the wrench flats...the Beer OUT post should not.

Gas IN post pic
Beer OUT post pic