Ping Zing irons. At launch, this was Ping's most extremely weighted iron - with a big deep cavity, and plenty of weight around the perimeter, resulting in a high moment of inertia (MOI). In simple terms, it means the clubhead resists twisting at impact on off-centre hits - so it is very forgiving. The deeply indented trailing edge helped reduce the surface area in contact with the turf while further increasing the perimeter weighting. Still highly useable and popular.