Take the widest face that fits the joint without bridging to adjacent pads or touching nearby components - approximately the width of the pad is a good working rule. Most people choose too small a tip and then compensate with temperature and dwell time. The widest tip that fits gives the fastest joint at the lowest temperature.

Contact area. Heat crosses into the joint through the area actually touching it, and a flat face delivers several times what a point can. That means faster wetting, a lower set temperature, less thermal stress on the board and better recovery between joints. A conical tip is the exception fitted when access genuinely prevents a chisel from reaching.

Loading the face with a small amount of solder and drawing it along a row of fine-pitch leads so each is soldered in turn by the moving fillet. It needs generous liquid flux and a steady pace. A chisel does this competently; bevel and hoof geometries hold a larger reservoir and are usually preferred where the technique is used constantly.

A copper core for conductivity, an iron plating over the working face to resist erosion by molten solder, and chrome plating on the shank so solder stays where it is wanted. Plating thickness is what determines working life. Never file, sand or scrape a tip - it removes the plating and the copper beneath dissolves quickly in solder.

They are the standard choice for them. Through-hole pads, stranded wire, connector tags, ground planes and anything with thermal mass need heat delivered faster than a fine tip can manage, otherwise the joint never reaches temperature and a cold or disturbed joint results. Choose the width from the pad and the mass behind it.