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 has it’s own locking latch mechanism. Made of fiberglass, so it can take much aduse both in cold and hot enviroment conditions.