Six people died at a Shenzhen amusement park in June because of a bad design that led to a broken bolt, the official investigation has found. The tragedy happened on the Space Journey ride, similar to a carousel but spinning nearly four times as fast to give riders, strapped in pairs in 12 capsules, the g-force sensation of a rocket's take-off. The capsules were fixed to swinging arms by a flexible fastening system - a sophisticated device with shock-absorbing pistons and springs - but nearly all the weight and stress went to a thumb-sized bolt that screwed into the top of the capsule. A report released by the Futian district Work Safety Bureau yesterday said it was a critical design flaw. To make matters worse, the bolt was located where maintenance workers were unable to inspect or reach it. One June 29, the bolt snapped due to metal fatigue and sent capsule No 5 flying off. It slammed into three other capsules, killing six people, including one Hong Kong person. Ten other people were injured. The report said the ride was poorly welded and this might have contributed to the casualties. The ride was designed in the mainland by an institute owned by the General Armament Department of the People's Liberation Army.