A Lecture on Soldering By The Soldering Craftsman 1-8

A standard iron head is included when a soldering iron is purchased. However, a standard iron head is not universal applicable.
However, in reality, most people including some soldering professionals would use the standard iron heads for everything. I have never seen the iron heads sold for replacement at Home-center hypermarket, which may mainly contribute to the fact that standard iron heads are often used for everything. In principle, different iron heads should be selected for different soldering purposes.

Changing an iron head not only affects the head profile, but also causes the change in thermal capacity, and even the same kind of iron heads may be different in the thermal capacity because of the difference in diameter.
As shown in the photo on the left, the iron heads are cut from a round bar at 45 degrees. From left to right, the head diameters are Φ0.5mm、Φ2mm、Φ3mm、Φ4mm、Φ5mm respectively. An iron head should be chosen in the light of the size of a mother metal (and its thermal capacity). A difference of 1mm in head diameter may make your soldering work surprisingly easy.
Contact area between the iron head and the worked piece is an important factor in deciding an iron head profile.
For example, the contact between two round bars in a cross way is merely a dot; the contact between a round bar and a flat is of linearity.

Iron heads are selected usually in the light of the sample books offered by the shops or trade firms. It is recommended that more types of iron heads be tried before mass purchase. Especially for mass production, difference in iron heads will be reflected in product quality and production cost.