help with bearings

One of the things we do in this house is write and edit math textbooks. For a lesson about circles, the author and artist have three bearings of different diameters: 2 cm, 3 cm, and 7 cm. The bearings are the usual type with row of balls around an inner surface. (The diameters I quoted are for the whole bearing, including the outer ring.)

So my question is, what do these bearings do? A quick Google search for bearings that size comes up with "cooling fans for computers," which is OK for one of them but pretty boring for all three.

Go to it, ladies & gents: plausible jobs for bearings in those sizes, please?

Roller skate bearings are a bit smaller than that, rear alternator bearing for 2cm, front alt bearing or clutch pilot bearing for 3cm, driveshaft support bearing for 7cm.

Bearings are sized according to the ID first, and the OD is determined by the series, or style of bearing. The ID should be quoted in mm not cm. That sounds like a typical ball bearing, and the inner surface is called the inner race. The outer is the outer race.

Streetwise, thanks! I'll check those out.

Zomby, fair points, and I appreciate the terminology (editors ALWAYS want the correct word) but for this application (a Grade 8 remedial-level book) we're just comparing radius to circumference. I'll find out if we can do mm instead of cm, but I think the project managers will say that the numbers would get too big.

small electric motors, casters, conveyor belt rollers, small pumps, bicycle hubs, blenders, rope sheaves,

Zombie annihilation turret gun bearings
Muffler bearings
Since accuracy isn't important, those'll be fun.

Where a rotating component is contained with a stationary component. Add appropriate pictures to suit the audience.

7cm O/D could be one wheel bearing

Thanks to all for the help. This board rocks.

A skateboard bearing might help keep their attention, can't comment on the sizes.

A 2 cm o/d bearing could be a wheel bearing for a 1/4 scale RC car.

RossD wrote: A skateboard bearing might help keep their attention, can't comment on the sizes.

If I recall from my son's skating days, that would be a 608Z. 8 x 22 x 7(W) with a (Z) steel shield instead of a seal.