XV4 = inner diameter + .637" or 16.18mm
The XV Model has a bit more room in the walls of the cup than the LX model has. It still features the shortened down overall length which reduces the amount of resistance offered. The #27 bore (.144 or 3.65mm) combines to make this model more open than most lead pieces. In this way the XV is unique, offering a semi-shallow cup while combining other resistance control features that make this model truly versatile offering a massive sound with lots of playability throughout the entire range, low to high.