The gong is used five times – to start class, to end class and to signal the three breaks.
This is a 12″ Zildjian gong. The nice folks at The Gong Shop in San Francisco suggest that a larger gong, probably 22-24 inches, may be best in terms of being very clear that something is about to happen. Some field experiments are called for.
Here’s another photo with the background edited out to show the the frame from which the gong is suspended.
Silver Wolf Wushu 