A fancy and beautifully made quill stem that fits 31.8mm center-area handlebars. It grips a bar stronger than single-bolt stems, which for heavy rides on trails and riding Bosco-Tosco handlebars, it's a fine way to go.
The four-bolt face plate makes it easy to mount or remove a handlebar, even all wrapped or gripped and cabled, belled, mirrored, and fog-horned. It's not a thing you have to do a lot, but if you like to change bars a lot, you'll like the convenience. There is a micro-'tingent of Rivendell people who swap bars like normal people breathe.
On the other hand, there are now four bolts to tighten properly--three more than usual. Pay attention.
Four lengths: 60, 85, 110, and 135cm but because the stem has a slight upward angle, the extension is a little shorter—the Vitruvian-man effect.
This is as good as stems get, and since it's one of the bike parts you'll look at the most often (ideally), it makes sense to go fancy. Actually $140 for a stem fillet brazed in Tokyo by the handlebar/stem experts is a screaming deal.
Tighten each M5 bolt 4 to 6 newton meters (2.9 to 3.68 ft/lbs) for a safe fit.
Cut and paste the link below for a $70 tool for that. Experienced mechanics can probably get by without it, but musclemen and raw rookies need one.