This sport-scale model of the KSR-420S flies on a cluster of three 18mm model rocket motors. The KSR-420S is easy to build and comes with ejection baffle, so no wadding is required. This makes it a great choice for rocketeers new to clustering. Dimensions Overall length : 27.475" Diameter : 1.637" (BT60) Fin Span : 6.21" Weight : 3.7oz Recommended Motors Estes 3 x A8-3, 3 x B4-4, 3 x B6-4, 3 x C6-5 Challenges: This rocket is pretty easy to build. The balsa fins are pre-cut. Decals are included. Requires (not included) Assembly, Wood glue, Hobby Knife, Sandpaper, Masking Tape, Primer, Clear Coat and Paint needed to build this rocket. Launch system with 3/16" Launch Rod, Cluster-Compatible Launch Controller, Igniters and Rocket Motors needed to launch this rocket and are not included. Recommended Motors Estes 3 x A8-3, 3 x B4-4, 3 x B6-4, 3 x C6-5. Since it is the cluster kit, we recommend it to people with previous rocket launching experience.