I engineered a 2mm micro-bearing D20 ring that free-spin for 20 seconds
Over the past few months I’ve been experimenting with how small a functional bearing-based mechanism can get while still feeling smooth, durable, and useful. This project started from a simple question: How thin can a real, free-spinning bearing be while still handling continuous rotation? Most “spinner rings” you see online cheat by simulating rotation — there’s no real bearing, just loose tolerance metal sliding on metal. True micro-bearing rotation needs precision, tight tolerances, and high surface finish, which is difficult when everything needs to be wearable on a finger. So I tried to…
In plain words
This is a wearable stainless steel ring featuring a genuine 2mm-thick micro-bearing mechanism with 20 steel balls that spin freely for over 20 seconds. Unlike typical spinner rings that rely on loose metal-on-metal contact, this design uses precision CNC machining with 0.01mm tolerances and a proper bearing track to achieve smooth, durable rotation. Made for anyone interested in mechanical fidgets or precision engineering, it stands out for using actual bearing technology in a functional finger ring.
written from the facts on this page · September 2026
From the sources
In the maker’s words, at launch
Over the past few months I’ve been experimenting with how small a functional bearing-based mechanism can get while still feeling smooth, durable, and useful. This project started from a simple question: How thin can a real, free-spinning bearing be while still handling continuous rotation? Most “spinner rings” you see online cheat by simulating rotation — there’s no real bearing, just loose tolerance metal sliding on metal. True micro-bearing rotation needs precision, tight tolerances, and high surface finish, which is difficult when everything needs to be wearable on a finger. So I tried to push it in the opposite direction and ended up making this: A 2mm-thick stainless steel ring with an internal micro-bearing track and 20 steel balls that free-spin for 20+ seconds with a single flick. Mechanical details: • CNC machined inner race with ~0.01mm tolerance • 20 micro steel balls loaded through a lateral channel • Outer ring pressed onto the bearing shell • No plastic, no bushings, no lubricant • Built to withstand everyday wearing forces (compression, torsion, micro-impacts) • PVD variant for color durability • Outer surface can be marked 1–20, turning it into a tiny randomizer Originally the goal was purely mechanical — to see if a bearing this thin could be made. But it ended up being surprisingly functional for solo tabletop RPG use: when you need a quick random result but don’t have table space, or when dice are too loud (playing in bed, on a commute, etc.). The ring spins silently and lands pointing at a single number. This wasn’t meant to replace dice; it just became a neat side effect of the engineering challenge. Why I’m posting here HN tends to appreciate: • micro-manufacturing • tolerances • machining challenges • precision mechanical design • unusual “why does this work?” projects I’d love to hear feedback on: • improving durability • minimizing friction losses • alternative ball materials • raceway finishing • any tricks for increasing spin time without adding thickness If anyone has experience with miniature bearings or wearable mechanical assemblies, I’d appreciate insights. Happy to answer questions about the build process, the tolerances, or the failures along the way.
More work this month
the category →
The app store for voice native apps that lives in your notch
Work · 28d ago · voiceos.com
The New Calendly▲211Handle all of the work before, during, and after meetings
Work · 17d ago · calendly.com
Launched alongside, November 2025
the whole month →
- IB
Life & fun · Nov 2025 · bitsnpieces.dev
- BBoing▲782
Life & fun · Nov 2025 · boing.greg.technology