Russian made Custom Arms folding stock extender. Basic extender adds 2 cm (0.78′) to the buttstock. Two additional spacers can add 1 cm (0.39′) each. So you can add total 4 cm (1.57′) to buttstock length. The extender allows the stock to fold and lock. It also allows to use standard locking button and kleaning kit storage. Made of fiberglass, so it can take much aduse both in cold and hot enviroment conditions.