Zenith 4-Position A3 Retractable Stock, Full Size 9mm MP5/Z-5RS. Constructed from strong steel with black finishing and a black polymer buttplate, this full-size 4-position A3 retractable stock is designed to install to Zenith roller-delayed firearms such as the Z-5, Z-5RS and other full-size MP5 variant firearms chambered in 9mm. This stock is installed with a large take down pin (sold separately) and easily slide to four different lengths via a button at the 6 oclock position. The small yet durable frame of this stock makes it an ideal addition to any full sized MP5 variant firearm and provides the shooter with a variable level of control to fit any and all shooting styles.