Brake pipe unions will not screw into place

[Wolfy]

Hey everyone, 

I am in the process of running new lines in the rear on my '06 Impreza, but have ran into an issue with the unions. I'm using 3/16 pipe with M10x1mm unions, but for some reason, after I have made the double flare, the unions will not screw onto the brake line or the junction box - well they do, but no more than one thread. If I tighten any further, it just unscrews itself. 

I have since learned that there is such thing as a short and long shoulder union. I believe the only difference is the thread length - is this true? If this is the case, surely, I would just have more thread exposed? 

I'm thinking about cutting my losses and just buying oem lines, to be honest. That leads me to another issue... the securing clips seem to be unobtainable. Does anyone know where you can get them? Or even the size of clip needed given the oem lines have plastic over them.

Thanks in advance - I'll add pictures of the unions and what not.

[Wolfy]

Problem solved. Short shoulder unions did the trick!

[Mr B]

they both shouldered same, 1 is long thread other is short thread.
other types are shouldered and no shoulder.
Is critical buy exact match to original when fittings going into original spec parts .
I've seen a few horrid repairs with wrong fittings catching by couple threads at most and risking peoples lives, some of those jobs done in licenced garages which even worse ...

[Wolfy]

1 hour ago, Mr B said:

they both shouldered same, 1 is long thread other is short thread.
other types are shouldered and no shoulder.
Is critical buy exact match to original when fittings going into original spec parts .
I've seen a few horrid repairs with wrong fittings catching by couple threads at most and risking peoples lives, some of those jobs done in licenced garages which even worse ...

The shorter one was sold as a short shoulder union and the longer as a long shoulder union, so I'm just going off that - and the fact the longer one won't screw onto the lines. I purchased some without the shoulder, which appear to be identical to the OEM ones.

I'm bypassing the junction box under the car and connecting the pipe under the back seat, as well as replacing the lines. Do you know why the new line has what appears to be a flat surface of sorts for the shoulder? The old brake lines didn't have this.

[Mr B]

Yes, short shoulder is basically not correct description.

you basically got 2 types shouldered or non shouldered and both types available in long or short thread lengths .

Exact match and good quality is a must on fittings, pipe and tooling .

I don't like copper pipe , copper/nickel is a better product and all i will use. lot of garages still use copper line but mainly as super easy/forgiving bend flare but it not long term durable and does work harden/crack .
 

[Wolfy]

5 hours ago, Mr B said:

Yes, short shoulder is basically not correct description.

you basically got 2 types shouldered or non shouldered and both types available in long or short thread lengths .

Exact match and good quality is a must on fittings, pipe and tooling .

I don't like copper pipe , copper/nickel is a better product and all i will use. lot of garages still use copper line but mainly as super easy/forgiving bend flare but it not long term durable and does work harden/crack .
 

Thanks! Yeah, I'm using copper nickel, not too bad to work with, to be honest. I put on the oem style union on - time will tell if I did anything wrong. I need to tidy the pipe up a bit, but I've had enough for today.