The OEM SRM wireless sensor provides transmission of cadence information and ignites and wakes upthe wireless SRM power unit. The simple design mounts under or around the bottom bracket shell of the frame. The usual way to set the cadence unit is to mount to the same hole/screw that the cable guide is a attached to. In more contemporary frames that do not have cables guides assembly via Velcro of double sided tape is required. These cadence magnets are required for all SRM wireless powermeters.