Technical Help! Brake fitting question

Replaced the master cylinder and now can't get this fitting tight enough. I dont want to snap it off which feels like where I'm at. Ideas?

 

Are you sure that you are using the correct fitting and/or the proper flare?

 

I think the hole is 1/8" NPT. If the fitting is also NPT, but worn, it might not have it's original taper any more, and won't tighten gradually like it should. In that case, you need a new fitting.

 

What Squirrel said!!!

 

Are you sure a single master cylinder is the right choice? While you were replacing the MC a dual cylinder would be a safer choice.
Just my opinion

 

If it's plumbed right and worked well till it was worn out, I wouldn't change a thing.

 

Is that a pipe thread in the end of the M/C? Or is it an inverted flare and an inverted flare fitting? If it’s an inverted flare, I think they make “seat savers” that go in before the fitting that might just shim it to a better position rotationally. I don’t remember where I’ve seen them but I was surprised to see that they make them.
If it’s just a common 1/4” pipe thread, sometimes you can tighten and loosen it a few times and gain a little rotation with each cycle.
Take the fitting out and take a picture of the end of the M/C.

 

Please tell me that you're not using an aluminum fitting in the master cylinder...