38mm – mattjfuller.com

The Apple Watch Series 1 models were similar to the original Apple Watch (also known as “Series 0”), but used a more powerful dual core processor. Like its predecessor, this Apple Watch was controlled with a Digital Crown and a Force Touch display, and it needed to be paired with iPhone 5 (or newer).

This Apple Watch Series 1 model is a 38mm version (a 42mm version was also available) and used a 272 × 340 display.

The Apple Watch Series 1 was originally sold in four standard configurations:
silver aluminum case with white Sport Band
gold aluminum case with cocoa (dark brown) Sport Band
rose gold aluminum case with midnight blue Sport Band
space gray aluminum case with black Sport Band

The Sport Bands were made of fluoroelastomer rubber. This Apple Watch Series 1 version has a silver aluminum case with white Sport Band.

Source: EveryMac.com

The Apple Watch Sport Band is made from a flexible rubber material called fluoroelastomer with a metal pin closure. Sizes range from S/M, M/L, or L/XL. When purchasing an Apple Watch Sport Band, the S/M and M/L sizes are included in the box, allowing the band to fit wrists 140–210 mm.

Apple describes the Apple Watch Sport band:

“Made from a custom high-performance fluoroelastomer, the Sport Band is durable and strong, yet surprisingly soft. The smooth, dense material drapes elegantly across your wrist and feels comfortable next to your skin. An innovative pin-and-tuck closure ensures a clean fit.”

The Apple Watch Sport band has been available in the most colors so far. As of November 2021, 110 Apple Sport Band colors were available with an additional 36 Nike Sport Band colors (according to the Bandbreite app).

This example comes with S/M and M/L sizes for the 38 mm Apple Watch that is also compatible with 40mm and 41mm sizes.

Source: Apple, Bandbreite app