Why does my u-joint have a button head fitting?

[6BangBronk]

Went to Advanced to get a new u-joint for my d44 shafts and bought the only greasable u-j they had and it has a button head fitting in the very center. Didn't even notice until I installed it for I've never seen a button head? Now I research and I need a $28 fitting for my gun to fit it? WTF!
I have now came to the conclusion (due to cost) to replace it with a regular zerk but I won't be able to grease it without pulling the shafts back out.

Anybody else have any input on the button head grease fittings? Why did they start using button heads on U-J's? Not even sure a button head grease fitting would fit without pulling the shafts anyways?

 

[snappy]

Pull the fitting out, put in a reg fitting, grease and replace the button head...

 

[ChrisAyers]

Had the same issue but I was able to find that grease gun fitting at O'reillys for $13, this was only a month or two ago so you should still be able to get it there for that price.

 

[6BangBronk]

Another tool to buy.

I guess if that's the best next thing, I need one. But for now I think the zerk swap will do and buy the thing when it's time to grease. Cool price though compared to what I've seen online! Thanks!