watchOS 5.1.3 (build 16S5523a) is an official Apple over-the-air update for the Apple Watch Series 2 (42mm), released on 2018-12-10T18:10:02Z. The update package is 67.28 MB. This is a delta (partial) update that requires 5.1.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 8bc98152903dab10e67750cc62ca1b9bc043bafa.zip.