The SP-A5 Spring and Buffer Kit includes everything you’ll need to outfit your rifle with VLTOR’s patented A5 Buffer System (aside from a compatible receiver extension tube). The SP-A5 kit is designed for the VLTOR A5 system and is only compatible with other VLTOR A5 products. This SP-A5 spring kit requires the use of an A5 receiver extension tube. Therefore, this kit is only compatible and should be used exclusively with a proper A5 buffer tube. The included buffer weight is a A5-H2 (5.3oz).