We looked for the smallest USB drive we could find: Super Talent Pico (and in gold for good measure).
The dimensions of the drive are published on the product page, which made shopping for lockets a bit easier before the drive arrived. When it did, we confirmed its max dimensions with calipers.
We shopped for lockets on Etsy, but the dimensions given were usually pretty spotty or not specific enough, so we bought three different inexpensive lockets to increase our chances that the USB drive would fit. This one ended up being perfect.
