The only 3-prong grounded "Duck Head" adapter for Apple power supplies on the market. Compatible with MacBook and iPad chargers with removable duck head. This is the only duck head on the market that fully grounds your computer. This means that the case of your MacBook will be fully connected to electrical ground when using. This has many benefits: it eliminates the annoying buzzing feeling felt on the MacBook in some situations. It also creates a much firmer connection to the wall, preventing your adapter from slipping out. It's also safer, especially when working in sensitive areas like medical facilities or around sensitive electronics. Also, as your palms rest on the computer, your entire body will be grounded or "earthed", which some claim has health benefits.