bought a multi task and the first head I got was the twin turbo blade which comes with a shaft. The part that goes to the head goes on really easy, no problems. The part that slides into the multi head fits really tight. Tried reversing the tube, doesn't work that. Put the shaft in to the head unit first with the lower part disassembled and the spindle out, but I am unable to get it to push into the coupler enough to get the pin to drop. I have twisted and turned, used deep creep, just doesn't want to go in. Anybody with one, with any ideas, I would deeply appreciate it. Regretting the purchase so far.