Altra Arrows Insert and Outsert .166 350 Spine Silver. 875" while the outsert then threads directly onto the insert and encapsulates the leading end of the arrow at 0.43" 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 Insert and Outsert: Manufacturer: Altra Arrows Color: Silver Features of Altra Arrows Insert and Outsert: Comes in 12 pk QTY Available in four sizes - 250 300 350 & 400 spine 50gn Total Weight Accepts micro FMS insert weights Package Contents: Altra Arrows Insert and Outsert Altra Arrows AA-SI-00003: Insert and Outsert .166 350 Spine Silver