This is an optional Exotek TLR 22-4 Carbon LiPo Battery Strap. Made of special matte finish 4mm thick carbon fiber, at 5gr each, each strap is almost 2gr lighter than stock. This is compatible with the Exotek twist nut/ lipo post set (EXO1501), and saddle pack batteries, and when using the team driver side rail modification can be used with shorty packs as well.