6201RS

• 6 - type code: single-row, deep groove ball bearing
• 2 - series / robustness: (2 corresponds with 'light', which is more durable than 0, but less durable than 3 or 4)
• 01 - size code: 12mm bore (inner diameter)
• RS - grease seal: rubber seal one side (no seal would be '6201', both sides sealed would be '6201-2RS'. Z and ZZ are used similarly to indicate presence of steel shield(s))

The 6201 is a good fit for this application, and providing the gerbil wasn't too hard on it, should last a long time.

So what do we think folks? Underbuilt angle grinder or overbuilt gerbil wheel?

Not all bearings are created equal. This might last for years. This also might explode into fast-moving metal shards in a day. It shouldn't be a big problem if it does, as an angle grinder should be built to contain exploding bearings, but it might be worth ordering a higher-spec bearing to have on hand before you need it in a hurry.

Those look like skateboard bearings to me, they are quite common. A relatively high quality set of 8 bearings is like 15 bucks if you have a skateshop nearby

That's either a very over-engineered hamster wheel, or that grinder was under spec'd.

That's a balls-y move.

They don’t make gerbil exercise wheels like they used to.

That's dope man!

What happened to your gerbil, op?

Your answer will be highly scrutinized.