From Prechtl web site

http://www.prechtl-waffen.de/Prechtl/de/Waffenteile/Mauser_Bauteile

Magazine cover Rigby II for Gewehr 98

This Rigbydeckel can be attached to every 98er who has the box with pushpins. The flat lid is replaced simply and without modifications by the Rigbydeckel. The original feeder and the feeder spring can still be used. The magazine capacity is increased, depending on the caliber, by up to 2 cartridges. The magazine capacity depends on the caliber and the condition of the original box. For installation, no gunsmith is required.

The cover is optional raw or finished polished and burnished available.