My headphone jack is the wrong size?

We are sorry to hear that you are having issues connecting your new headphones.  
 
Many headphones come with a 3.5mm connector, however, some audio equipment will feature ¼ Inch sockets. 

As such, all Gear4music branded headphones, and many other branded headphones include an adapter so your headphones can be used with either size socket. 
 
This can be found inside the packaging of your headphones.