Brake Disc Upgrade Kit – To fit Revvi 12″ and 16″ kids electric balance bikes Please note – 15mm CONE/THIN SPANNER IS REQUIRED TO FIT THIS KIT, You may also need to slightly adjust the rear wheel spacing with washers for the perfect fit/alignment. A rear cable disc brake kit designed by Moto Twenty5 Concepts to both improve brake power and also ease of use for the rider.The kit works with your standard brake lever and cable and will fit both 12″ & 16″ standard bikes and includes: rear caliper 140mm disc brake disc hub mount brake mount nuts/bolts/spacers/ties