From Trango's Website:
"The Harpoon™ is a high performance rigid frame waterfall crampon built on the time tested vertical rail design, but that doesn't even begin to describe the Harpoon's™ performance or versatility. Use it in the dual-point configuration and you'll find it's a stable, precise and sure-footed crampon, capable of getting you up any icefall in the world. The forged points have a “T” profile so they resist shearing through soft ice and they’re completely vibration free.
Install the optional Mono-Point Conversion Kit and the Harpoon™ becomes a foot weapon, lethal to the hardest, steepest and thinnest mixed climbs on the planet. That's because the asymmetrical design of the mono-point puts the power where you can control it...right under your big toe. Imagine that…a crampon designed to work with your foot! The geometry of these is such that by splaying your feet out naturally, both the mono-point and the inside secondary point engage the ice (or whatever) giving you the stable platform of a dual point. Turn your heel out a bit, however, and you have all the precision and versatility of a mono-point.