Mercury - Quicksilver 818883A1 Thumb Screw Assembly Kit Mercury 25-30HP FourStroke & 40-60HP TwoStroke Outboards 818883A1. Overview. A fresh set of transom thumb screws can make your outboard easier to adjust - and look sharper while doing it. The Mercury 818883A1 Thumb Screw Assembly Kit restores both the appearance and function of your engine's transom bracket.. Built with durable stainless steel screws and a sleek chromate-finish handle, this OEM kit is made for Mercury 25-30HP carbureted Fou