do all bands fit all watches

I am a woman with a small wrist, but I have the 42mm watch face. Can I buy either a 38mm or 42mm for that watch?

Hi

Any 38mm or 42mm Apple Watch band will fit an Apple Watch of the same size.

Apple Watch Sport currently includes a band that offers both S/M + M/L size configurations (a longer length Sport Band is available separately in certain colours).

Non-Sport bands have different sizes (and it is also possible to buy extra links for the 42mm Stainless Steel Link Bracelet).

Check your wrist circumference and refer to the Apple Watch Sizing Guide (which compares all Apple bands) before buying separate bands:

http://www.apple.com/shop/watch/sizing-guide

The Apple Watch Sport also has an anodized aluminum case, whereas non-Sport bands have different metals in their adapters and/or links.

See here for help on how to change bands over: Change your Apple Watch band - Apple Support

You're incorrect. I'm currently using a 42mm face with the 38mm silicone band I had from my other watch. I wanted a bigger watch face but because I have smaller wrists I had to use the old bands.