Kit is recommended for a bottom bracket replacement on bikes that have a bottom bracket with the square tapered shaft. Some bikes in the field require a change of the crank arms when this bottom bracket is installed due to incompatibility of some arms to the bottom bracket. There are no manufacturer dates or serial numbers available to determine if crank arms require replacement. This bottom bracket and crank arm kit contains the bottom bracket and both left and right crank arms. Reduce any extra downtime that could be created by needing more parts and purchase your bottom bracket and crank arm kit today.