Which SRAM flat mount caliper bolt length do I need — 27mm?

The 27mm Flat Mount stainless steel caliper bracket bolts are the correct fasteners for direct flat mount brake installations where the caliper threads straight into the frame or fork's native mount without any intervening adapter hardware. This is the standard bolt length for most road and gravel frames with a built-in Flat Mount interface — when the rotor size matches what the frame's mount is positioned for, no adapter is needed, and the 27mm bolt has the right thread engagement for safe, secure caliper installation. Stainless steel construction resists the corrosion and thread seizing that standard steel bolts develop in aluminum caliper mounts after regular wet-weather riding, where salt and moisture turn routine bolt removal into a stripped-thread situation over time. Drive is T25 Torx for proper torque application.

These are sold as replacement or spare hardware, not bundled with a caliper. If you are building a disc brake road or gravel bike with a native flat mount interface, replacing seized or stripped bolts, or maintaining your service bench stock, these are the correct stainless fasteners at the 27mm direct-mount length. If your setup uses a bracket adapter to accommodate a larger rotor on a smaller mount, you need the 37mm version instead. Bolt length matters on flat mount brakes — too short won't torque properly, too long bottoms before clamping, so verify your application before ordering.