Hi all. I am having an issue once i tighten the coupler and after several runs i back the nut off the coupler i really have to pull hard to remove the 3/16 flex shaft . I always solder the last 1/2 inch off the shaft and bevel the end of the shaft the collet to flex shaft alignment is perfect i even chucked the end of the shaft that goes in the collet in the lathe and ran a emery cloth across the end in case of a burr i slid the shaft in and out of the collet 10 times no problem once i tightened the coupler nut and backed the nut off again same problem i really had to pull hard to pull the shaft out again and i could not see no problem with the inside of the collet either ! WHAT ELSE COULD BE CAUSING THIS PROBLEM ?In my 46 yrs of r/c boating i have used H&M Aeromarine and Octura couplers and never had this kind of problem .Regards Andris Golts