Includes 27 parts to build engine Mounts. Perfect for the do-it-yourselfer! 27 pieces each. Bt5 body tube. 2 inches long. 3 each. Bt5 yellow engine blocks. 3 each. Bt5 Mylar engine hook retainer rings.3 each. Bt20 body tube. 2.75 inches long. 3 each. Bt20 engine blocks. 3 each. Bt20 Mylar engine hook retainer rings.3 each. Bt50 body tube. 4 inches long. 3 each. Bt50 yellow engine blocks. 3 each. Bt50 black engine hook retainer rings.