I’m on my 2nd set of Cobra single length irons (wore out 7-GW faces of the Forged Ones) and have just had the 5th shaft one break at the hosel (all KBS Tour Steel).  I’ve been a Golfworks customer for 35+ years.  I cannot recall a steel shaft ever breaking there before, even in my harder swinging youth (I’m 75, now).  Putting in perspective, my clubhead speed with my irons in in the 85-90 mph range (165-170 yds with 5 iron).  Just eyeballing, it looks like the shaft wall of the KBS shafts is much thinner than I ever remember my beloved tapered tip TT Gold Dynamics, my shaft of choice for years.  Could this thinner wall be the cause?  I’ve always figured steel shafts good for 20 years or more, not 18 months.  Fortunately, in 4 of the 5 breakages, Cobra has faithfully repaired them under warranty.  Gunshy, I’ve recently bought a set of conventional length new Ping i’s with Recoil shafts.