If you want to skip this writeup about watch band compatibility, I found an image from chargerstore on eBay that sums it up beautifully in just one image:

If you want the nitty gritty, keep reading.

Apple Watch Series 10 hits several new milestones. As usual, it’s the best Apple Watch since Apple Watch, with an even bigger screen that matches the size of the Apple Watch Ultra. Apple says it’s bigger than the Ultra, but to the naked eye, it is the same.

There is one more milestone for the Series 10 that is not discussed.

The smaller 42mm Series 10 is now the same size as the bigger version of the original Apple Watch. The Series 10 is thinner, but the length and width are the same.

*The Series 3 (same design as the original Apple Watch), measures 42mm x 36.4mm, and the Series 10 measures 42mm x 36mm.*

This now begs the question:

If they both have a 42mm case size, are all 42mm bands that Apple sells or has sold in the past, interchangeable with both these watches?

The short answer is no, but let’s really dive into the details.

If you look at the Series 3 (and older), it is much more square in shape while the Series 10 has more rounded off corners. That square body of the Series 3 adds extra real estate and needs a wider band to fit into the slots.

*Not all 42mm case sizes are created equal.*

When you’re about to buy a watch band on Apple’s website, there is a link showing compatibility details.

Here is part of what it says:

You can match most bands with any Apple Watch Series 3 or later case of the same size.
38mm, 40mm, 41mm, and 42mm bands are compatible with 38mm, 40mm, 41mm, 42mm case sizes. 44mm, 45mm, 46mm, and 49mm bands are compatible with 44mm, 45mm, 46mm, and 49mm case sizes.

The first sentence is a bit misleading because a 42mm Series 3 will be compatible with the new 42mm bands that Apple sells today, but there will be a gap on each side:

The gap isn’t a deal breaker and can be perfectly usable and presentable. You might even forget the gap exists. Might.

At the same time, if you are buying a 42mm Series 10 Apple Watch, and you want to scour the internet for some classic bands that Apple used to sell, you might get burned buying a rare band that is 42mm, only to realize it is bigger than your Series 10:

This is how Apple should word their compatibility description:

You can match most bands with any Apple Watch Series 3 or later case of the same size.
38mm, 40mm, 41mm, and 42mm bands are compatible with 38mm, 40mm, 41mm, and Series 10 42mm case sizes.
44mm, 45mm, 46mm, and 49mm bands are compatible with 44mm, 45mm, 46mm, and 49mm case sizes, and Series 3 or earlier models with a 42mm case size.

I know what most of you are thinking.

“Who actually uses a Series 3 or earlier Apple Watch??”

Last week, I saw someone using an iPhone 5S as their main device. It had the polished chamfered edges and not the matte-finished edges of the 1st gen iPhone SE.

If you know, you know.

If people can still rock an 11-yr-old iPhone 5S as their primary communication device, they sure as heck can rock a 7-yr-old Series 3 Apple Watch as a secondary, “no problems if I forget it at home,” device.

I have been wearing a Series 3 for over a week now, and it is still usable today, but we’ll take a deep dive into that another time.

Like I said earlier, the main issue isn’t really for Series 3 users since you can get by with a slimmer band. The problem is for 42mm Series 10 users who want to buy older bands or discontinued leather bands that are labelled 42mm.

Let’s not forget about 3rd party bands either, which only compounds the problem.

That being said, here are the rules for buying watch bands for your 42mm watch:

Series 3 or earlier - Look at the item description. If 42mm is paired with numbers above it (44mm, 45mm, 46mm, 49mm), it is compatible.
Series 10 - Look at the item description. If 42mm is paired with numbers below it (38mm, 40mm, 41mm), it is compatible.

If they advertise the band as 42mm by itself, God help you.

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