The M21143 dowel pin is an interesting study. According to the published description, “Dowel pins covered by this spec are intended for use in machine applications employing light drives for torque transmission, positioning parts with respect to one another, and for fastening together two or more parts of an assembly.” The drawing/specification NASM21143 is published by the Aerospace Industries Association and is actually a procurement specification while the associated dowel pins are the NASM21143/1 (standard size) and the NASM21143/2 (.0002” undersized). Both pins are made from 303 S.S. and require passivation, but if you thought that’s all there is to it, you’d be wrong. They are both subject to the NASM21143 procurement spec, which carries a boatload of extra requirements:
The procurement specification covers headless straight pins of the following classes…
Class 1: .0002 inch over size
Class 2: .001 inch over size
Class 3: .0002 inch under size
…and pertains not only to NASM21143/1 and NASM21143/2 dowel pins, but also NASM16555 and NASM16556.
While the former two dowel pins require 303 S.S., the latter two, depending on their dash number, can be made from Carbon or Alloy Steel, Austenitic Corrosion Resistant Steel (e.g., 303 S.S.), or Martensitic Corrosion Resistant Steel (e.g., 416 S.S., 410 S.S.). Once again, depending on their dash number, they may or may not be heat-treated, phosphate coated, cadmium plated, passivated, or furnished with a plain finish. They are all subject to double shear force testing, straightness requirements, a maximum surface roughness (on the cylindrical surface) of 16 micro inches Ra (Roughness Average), and roundness requirements.
When you encounter a requirement for a M21143/1 or M21143/2 dowel pin, don’t dismiss it as “just another commercial dowel pin”; as you can see, there’s much more to it when you read the fine print.
Let Horberg Industries be your trusted source for all things NASM21143…you’ve got enough on your plate!
Horberg Industries…Dowel Pins Made Right!