Cox also built Tee Dee's in.010 (Cat#130),.020 (Cat#160),.09 (Cat#210) and.15 (Cat#180) size. All these engines were very successful. The original Tee Dee 15 immediately became the engine to use in FAI FF with vastly higher performance than the Olympic, which had supplanted the European diesels used at the time. They proved fragile, particularly the thin-wall cylinder, and ball-and-socket connecting rod, and were replaced by beefed-up versions (as noted below).