Here's a wood prop that came loose from a friend's plane this week. All 6 prop bolts sheared off; I think he failed to torque them down often enough. The spinner and center bolt remained intact and this allowed the spinner to chew into the prop. The spinner cut about 1/3 of the way through each blade before he got it shut down. This damage happened in about 30 seconds. The engine continued to run after the bolts sheared off.