watchOS 5.1.2 (build 16S5042a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-11-07T21:14:51Z. The update package is 209.82 MB. This is a delta (partial) update that requires 5.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9dc7d086c5fd090b62c8c8b000f22d26d127004d.zip.