GREENSBORO, N.C. (AP) — Anyone who's served in the military, worked for the federal government or addressed a package at the post office is probably familiar with an iconic government pen.

But they might not have realized it was made by the visually impaired for the past five decades.

The ubiquitous SKILCRAFT U.S. Government pens turning 50 this month.

National Industries for the Blind traces the pen's history to April 20, 1968, when it was introduced to government buyers. The nonprofit organization was tapped to supply pens after another manufacturer made 13 million defective ballpoints in 1967.

The pens must be able to write a continuous line 1 mile (1.6 kilometers) long and keep the ink flowing despite extreme temperatures — from 40 degrees below zero to 160 degrees (4 to 71 degrees Celsius).

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