About alloy shields: These are the same high quality alloy bearing shields that come with all of our BBInfinite modules for use with 30mm spindles. Replacement bearing shields work with both Road and MTB bikes.
About Shimano top hats: These polymer "top hats" work with all 6805 bearings in all BBInfinite one-piece modules for Shimano and Gxp, all threaded bb's for Shimano and Gxp, and all Trek BB90 Kits for Shimano and Gxp. Shimano bb's use a pair while Gxp uses only one on the drive-side.
For complete Gxp parts kits, go here.