Plenty of accidents can happen on a mountain bike. Ramming your family jewels into the bike stem during a sudden stop is one even careful riders can get into. The Stemie won't stop that from happening, but it can severely dampen the impact when the bike stem crashes with your baby-maker.
If all you do with a bicycle is commuting, the chances you'll need this is slim. Those who push pedals for adventure and sport, though, will likely know the danger all too well. One minute you're riding downhill; the next, you're hitting a rock and getting your nuts whacked on a strip of solid steel. Not cool.
The Stemie is a silicone rubber fitting that's designed to strap around your bike's stem. It covers the whole thing, so that when you slide into the front of the frame, you'll end up slamming into a softer surface, hopefully leading to less damage in your sensitive areas.
Weighing 2.1 ounces, it comes in a single size, but is stretchable and moldable to go over a wide variety of protruding bike joints. They don't present any data about how much less of an impact you can expect, so we're not sure how drastic of an improvement it actually is. Given the choice of that body part coming into hard contact with steel or a rubber-covered steel, though, I guess I'll always take the latter.
"Use a Stemie and ride hard," that's what the product's official website says. If you're really worried about crotch-vs-steel accidents, though, we urge you to wear a protective cup, as well. The Stemie is available in a variety of colors for $19 each.