The Tri-Pen Company was founded in Rhode Island with consummate bad timing, at the very beginning of the Great Depression. Their Triad triangular fountain pens were made to the highest standard of quality, but few were made and even fewer survive intact. The Triad's design was simply too clever to be practical: the cap did not simply pull off, but was held on by screwing down the crown of the cap. Anyone attempting to open a Triad and not knowing the trick would first give the cap a pull, then would give it a twist, shattering the cap. For this reason, most collectors find Triads with repaired cap lips entirely acceptable, as long as the restoration is well done. The best technique to use when opening a Triad is to turn the cap crown with one hand while holding the cap body with the other. The hand holding the cap body can also grip and support the barrel at the same time, but the main grip should be on the cap in order to avoid twisting the cap in relation to the barrel.
Matching triangular pencils were also offered; production of the pencils continued for some time after pen manufacture ceased. Note that other triangular-section pencils are sometimes misrepresented as Triads. Real Triad pencils have the very distinctive "TRIAD" marked arrow clip with a triangle logo near the top; note the fancy banding at the ends, as well, and the overall solidity and attention to detail.
Most Triads were colorful, but basic black was also offered -- though rarely seen. Triads are often found in standard celluloid patterns of the era, such as black and pearl and jade green, but turn up as well in more exotic materials used by other New England penmakers such as Leboeuf and Chilton.
Triads are so scarce that assembling a single-brand collection of any size would be nearly impossible. Just about every collector would like to have an example of this singular design, however -- so if you get offered a Triad, don't pass it by lightly: the next opportunity may be a long time coming.
UPDATE: Jonathan Veley's research on Triad pencils has revealed that their distinctive triangular shape was originally adopted to promote Triad radio tubes, which were packaged in a distinctive triangular box. The pencils therefore preceded the pens, and were originally produced by the Rex Manufacturing Company -- whose owners were also the owners of Triad, the radio tube makers, and the founders of the Tri-Pen Company. Read the full story here.