for SRAM RED 11-speed 11/30 cassettethe original 30T cog can be replaced with a cog with same number of teeth, an ARI 30T cog, or with an upgrade ARI 32T or 34T, without any additional modification on your bikereplacement is easy and fast material used is ERGAL 7075T6 hard anodizedthe range of colors is available in the color chartweight of 30 teeth cog is 38 gramsweight of 32 teeth cog is 42 gramsweight of 34 teeth cog is 46 gramsweight of the original SRAM 30teeth cog is 41 grams