The reverse of what we usually look for in a headphone adaptor – this one is perfect when you’ve got a 1/4″ plug, and need to squeeze it into a 3.5mm socket.
The vast majority of headphones come with 3.5mm as standard, supplied with an adaptor to turn it into 1/4″ if required. However some brands, such as Fostex, simply have the 1/4″ as standard.