The bit type is determined by the soldering iron it is used on. There are screw type bits (bits that screw onto, or into the solder iron element), slip on bits that slip over the element and plug type bits that slide inside of the element. There are even bits that are a permanent part of a replaceable element/bit assembly. Regardless of the type of bits required it is always important to have them fully seated to the element and periodically cleaned, in order to maintain proper heat transfer from the element into the bit.
ConfigurationThe bit configuration to use should be determined by the intended application requirements. Some of the basic bit configurations available include ballpoint, conical, diamond (pyramid), chisel, and spade. You will find that there are usually a variety of styles, or modifications available, within each of these basic configuration families, to accommodate specific application requirements. Although less efficient, a more narrow configuration is sometimes required to obtain accessibility, or to achieve the desired results.
SizeThe bit size to use (regarding the working portion) should also be determined by the intended application requirements. The bit body, or shank must be matched to the iron it will be used with (always select a bit that was designed, or approved for the soldering iron you intend to use on the application being considered). As with bit configuration though, there are usually a variety of modified working diameters available within each family of standard bit sizes that are available. These modified bits are generally referred to as turned down bits, because the working area of the bit has been turned down to a smaller diameter than the body, or shank diameter. Turned down bits are not as efficient, but are sometimes required to solder in otherwise inaccessible areas.
Courtesy American Beauty Tools