https://www.outdoorgearbarn.com/p-9622-warne-m848848m-base-set-win-sxr-mat.aspx

Warne Matte Black Base Set For Winchester Model SXR Maxima alloy steel bases are made by the same process as the Premier bases but have the Weaver dimensions profile. They provide a strong alternative to aluminum and are attached with high tensile strength Torx-style screws.