This is the Standard Engine Mount Kit by Estes. Suitable for Ages 10 & Older with Adult Supervision for Those Under 12. FEATURES: Regular engine mounts Easy to assemble with complete insturctions Kit fits BT-50, 55 and 60 tubes Can be used to make a conversion mount for lightweight D powered rockets INCLUDES: 20/55 laser cut centering ring set 20/60 laser cut centering ring set 20/50 adapter ring 20/50 split adapter ring Engine blocks Engine hook retainer rings Engine hooks Engine mount tubes REQUIRES: Hobby knife (RMXR6909) Sandpaper 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 kr6/21/01 ir/jl updated tlc 1/10/13