They are pretty fragile, in my experience. When I first got mine, I loaded a stem while it was beating, filled stem, inserted stem, it broke. Just snapped above the glass "basket" area. Several broke this way my first week ( I got an Air at the same time, they were also breaking). I'm pretty careful with things, so I wasn't being rough or dropping them. I've also haven't broken any other glass in the time I've been using cannabis, so I was surprised at how easily the stems broke. While I liked my Solo and Air, I wasn't using them much because of fear of breaking my remaining few stems. I ordered two stems from
@Ed's TnT , and now my Solo and Air are in heavy rotation ( I alternate while one is charging, and use the other). You might be luckier than I was, and I am in no way disparaging the Solo or Air. I just don't worry a second with my Blackwood stems. If they haven't already "paid for themselves", by my not having to replace glass stems, they soon will. They also don't get hot on my lips, and can be used as WPA with 14mm glass.