My fairly new Sennheiser 600's have a 1/8" mini plug and came with an adapter to 1/4".
Sennheiser replacement cables
It's interesting that the Sennheiser HD580 and 600 use the same replacement cable, h-81435, while the 650 uses the h-92885. The 650 replacement cable is actually a bit less expensive than the other cable, and I've been told it's a better replacement cord for all 3 models. Any thoughts? Thanks