Shipped
Open Specs and parts on a car or bike and tap New beside Parts. A name is all a part needs, like "Garrett GT2860 turbo kit". Add the date and mileage if you know them, and a part number or notes under More details.
When a part went on during a job you log, add it under Parts on the maintenance record. The part takes the record's date and mileage, and the record keeps the cost and receipt photos. Edit an older record to add a part you put on before.
Pick what a part replaced under Replaces, one part or several for a kit. The old ones move to Removed parts with the dates they were on and the miles they covered. A bike's groupset is a part too, so an upgrade from Shimano 105 to Ultegra keeps both.