This is the 24mm to 29mm Engine Adapters by Estes. Suitable for Ages 10 & Older with Adult Supervision for Those Under 12. FEATURES: Very simple transformation of an Estes 24mm casing into an Estes 29mm casing size Reusable Adapts Estes 24mm C11/D, Estes 24mm E and Estes E30 series composite engines to a 29mm Estes casing size 2 sets per Orange adapter tubes included also Illustrated instructions included INCLUDES: Two 24mm to 29mm Engine Adapters COMMENTS: Due to small parts that could cause a choking hazard please keep away from children 3 years of age and younger For your safety and enjoyment, always follow the NAR Model Rocketry Safety Code while participating in any model rocketry activities Features Made of durable materials 24mm to 29mm Specifications Size: 29 mm