I ordered a defy with a 3/8-10 joint, waited 11 month for it, then could NOT screw it all the way down on a Mcdermott D5, D8 or OB Cue all with 3/8-10 pins. It started out difficult then and got to the point where I was unable to finish the last 2-3 turns. I'm in my late 60's and have arthritis in my hands. I called Mcdermott and was told they are now using a different style 3/8-10 pin/joint. Was told to work the shaft on/off and it would eventually work on the older style 3/8-10 joints. Went to the local pool room and had a younger player screw the shaft on/off 25-30 times before I could finally do it. After putting it on/off myself 700-800 times it still difficult to finish the last 2-3 turns.
I like the way the shaft played and ordered another one. Same issue. I called Mcdermott and they provided me a UPS shipping label. I sent the 2nd shaft back to Mcdermott along with the D5 butt and they did something. The 2nd shaft now screws on the D5, D8 and OB butts with no problems.
I've used several different shafts on these butts (Mcdermott maple, G-core, I-3 shafts. OB shafts, Predator shafts and Hsunami shafts) and never had this problem except with the Defy..