here is another way--take a rat tail file and make a few passes down the inside. then install ferrule with a little epoxy and using the head that goes on the shaft move the ferrule down a ways (it wont come close to seating yet) then take your heat gun on low setting and twirl the shaft keeping the ferrule about 6inches away from the heat and all the heat towards the top of the ferrule not the middle---about 6 seconds only and the head can be placed back on the shaft and seated very easily ---this way you can use tapered ferrules and they always seat tighter and youll never ever have one come loose ---as for selections of tapered ferrules there are are just as many or more than .370 and also you can almost always get OEM ferrules if you know where to look hope this helps bushkin