I have plenty of them, crooked fins, epoxying fins to an alignment jig. Today I pulled one of my biggest oops! Working on a Estes Plasma probe and nearly had it completed. I took out the little plastic bag that had the shock cord, chute, and ~gasp !~ the engine stop block! Yep the entire model was assembled and I had forgotten to put the stop block in there! Fortunately the design of this model has a short lower section BT55 about 4 1/4" to the top of the motor tube. I managed to mix some 30 minute epoxy for plenty of working time, slipped the stop block on the end of a small screw drivers handle and putzed around with it forever getting it lined up and pushed into place, but I did get it in there! If it had been a smaller or longer tube I woulda been stuck!