Dowel Pins are a hardened and precisely shaped pin used to keep machine components in accurate alignment they are also used as location guides for adjacent machine parts and to keep the two sections of a punch and die in alignment. For a tight fit your hole should be equal to or slightly smaller than the diameter shown. The length of the dowel pin is the overall measurement Length: Dowel Pins length is measured overall Material / Coating: Black or plain finish is unfinished (bare steel) has no actual protective coating. There may be an oil residue which provides some shelf life but no real corrosion protection when in use. The term “black” is an old industry term for plain. All material is advisory only and its use by anyone is entirely voluntary. Reliance on it for any purpose by anyone is at the sole risk of that person and Bolt and Nut Australia is not responsible for any loss claim or damages arising therefrom.