I went to AutoZone to get a flaring tool for my 3/8" and 1/4" tubing. Funny story about the tubing... I had to get it from Advance Auto since AutoZone is trying to sell me brake lines designed for my car even though I told the dumbass it's NOT for my car. Why do they always do that!? ... anyway I got a metric flaring tool from AutoZone and I was hoping someone could help me out. The thing goes up to 10mm which isn't 3/8" but it's very close. Would it be safe to go ahead and use the metric version? Or should I try and find something with standard measurements? I just want to make sure that if I use the 10mm that my AN fittings and stuff don't leak fuel all over my headers

Thanks,
-somebody

 

Standard AN fittings require the use of a 37* flaring tool. Using a 45* SAE or DIN or other flaring tool WILL result in leaks and failure...
Your post confuses me a bit as the majority of braking systems do not use the AN 37* flares. Most would use 45* double flares.
Some braking set-ups do use AN flares. The Camaro I am currently working on will use a good amount of 37* flares in it's braking system.

be aware a good amount of parts store flaring tools will not work with stainless steel.

EASTWOOD has a good assortment of flaring tools. I bought some of the tools I have from Aircraft spruce (aircraft supply house) and others from eastwood and the Snap-On truck.

 

The mild steel tubing is welded, with a seam on the ID. Therefore, it's necessary to make a double flare, so the seam is not in contact with the seal surface of the joint...
Seamless stainless is single flared.