When it comes to hardlines in your engine bay, there’s no such thing as “good enough.” Either your flare is awesome and it seals, or it doesn’t. Chances are if it’s being run through a hardline, it’s not something that is very tolerant of “good enough” anyway.
While usually associated with brakes, getting under the hood, the most common substances carried by hardlines in a performance application are fuel and nitrous oxide. No one wants a leaky fuel line, and at the operating pressures of nitrous oxide, even the slightest imperfection in your mating surface can mean a pretty severe leak.
While that used to mean spending tons of money on a high-end flaring tool or paying someone else to do it, altogether, with the advent of Koul Tool’s Sureseat P-51 tool, every flare seals like a perfect flare. The P-51 tool is not a flaring tool, but rather a lapping tool, designed to make a perfectly flat 37- or 45-degree sealing ridge for perfect seal every time.
The incredibly-easy-to-use tool simply requires you to fit the appropriate abrasive lapping head (37- or 45 degree), fit the proper collet onto the tubing (3/16-inch to 1/2-inch diameters), and then fit the collet and tube assembly into the yoke. Add a little lubricant to the lapping head, apply some pressure to the spring-loaded lapping bar while rotating the head back and forth to cut a perfect seat — much like when lapping a valve and valve seat.
The tool makes every flare a perfect flare — as long as you remember to put the nut on before you make the flare (no tool can fix that one). And, if by chance you need to clean up the male flare fitting, the P-51 is the perfect complement to the Koul Tools Fitting Fixer, which does the same thing, but the inverse.