Twin Cracks is a wonderful hand crack. The crux is in the middle of the climb, where the left crack gets a little wide. It's another classic climb in at Upper Sullies. I really like this climb, it was my first crack climb. And was the start of an addiction to crack climbing.
Just to the right of S crack. It's pretty obvious. You can either rappel into the canyon or there is a walk down by the pipeline a little farther down canyon.
cams .75-3 bring some small chalks for the right crack. Like all of the climbs at Upper Sullies there is no fixed anchor, but it's pretty straight forward to use trad gear to build an anchor.