In my tap and die kit is a thread gauge:



I can use this to gauge the threads of bit tips.

Tim, if you can get one of these, you can measure your bits and tell me the thread spacing and I'll look for one for you that is coarser or the same.
Just let me know....

Tom and I measured some of the bits we have on hand here and some are 12 and others are 14. There may have been one less then 12 (which is the coarsest gauge on the tool). The higher the number the finer the thread on the lead screw.