Altra Insert and Outsert.166 300 Spine is a precision arrow component designed for archers who tune spine and weight to achieve consistent flight. This 12-pack provides flexible tuning options with four spine sizes and compatibility for micro FMS insert weights, making it easier to dial in your arrow setup.

• Pack quantity: 12 pieces per package for replacement and experimentation
• Spine sizes: Available in 250, 300, 350, and 400 spine to match varied shaft stiffness
• Total weight: 50 gn total weight to enable incremental tuning
• Micro FMS compatibility: Accepts micro FMS insert weights for precise balance adjustments
• Component type: Insert and Outsert design designed to integrate with compatible arrow systems

This setup helps archers improve consistency by enabling precise front-of-center balance and weight distribution to suit your bow speed, draw length, and shooting discipline. The four spine options let you pair these components with a range of carbon shafts, while the micro FMS insert weights let you fine-tune without swapping entire components. Ideal for serious target shooters and anyone seeking more predictable groupings and repeatable results from their arrows.