Altra Arrows Inserts and Outserts for Altra 204 Arrows 350 Spine Set of 12 Black. R.C.O.S.) fits our Altra Arrows 204 Shafts and are machined out of 7075-T6 aluminum for unmatched durability and performance with optimal fit options. The insert secures into the arrow shaft at a depth of 0.875in while the outsert then threads directly onto the insert and encapsulates the leading end of the arrow at 0.43in creating unmatched durability. Essential rubber O-rings come pre-installed on the insert within the A.R.C.O.S. as they aid in locking the outsert in place which reduces vibration and improves concentricity between the outsert to the insert for a more precise arrow set up and down range accuracy. Specifications for Altra Arrows Inserts and Outserts for Altra 204 Arrows: Manufacturer: Altra Arrows Color: Black Fabric/Material: 7075-T6 Aluminum Features of Altra Arrows 204 Insert and Outsert: Fits Altra Arrows 204 Shafts Constructed from 7075-T6 aluminum for durability Secure insert depth: 0.875 inches Outsert encapsulates arrow end: 0.43 inches Pre-installed rubber O-rings reduce vibration and improve concentricity Comes in 12 pk QTY Available in four sizes: 250 300 350 & 400 spine 53gn Total Weight Accepts micro FMS insert weights Enhances downrange accuracy and precision Package Contents: Altra Arrows Inserts and Outserts for Altra 204 Arrows Altra Arrows AA-SI-00013: Inserts and Outserts for Altra 204 Arrows 350 Spine Set of 12 Black