Maverick and Spectre Upgrade Spring (6+ Kg) 6kg custom fitted upgrade spring. Compatible With: Maverick (4kg stock) and Spectre (4kg stock). Mod at your own risk! Increasing the spring tension can break or damage stock internal components of your blaster. Some blasters are extremely hard to reassemble, and we won't be able to troubleshoot problems due to user error. Blaster not included.