0.355 taper i believe but if they are like x-14s they are also press fitted. Makes them difficult to pull. Some people ream them to 0.370 to solve this. I found pulled Callaway shafts on ebay to do mine.The up grade from the uniflex shaft was good. Went to rifles.

To double check go to golfsmith.com and check clubmakers section. There will be info on OEM shafts there.