The second cap on my Nikon TC20 teleconverter is jammed on. Not the\nnormal fat black lens-back cap but the other one that's gray & flatter.\nIt twists counterclockwise to loosen but won't come off fully. It ought\nto unscrew clockwise to remove according to the arrow on it. When\nloosened it'll lift up partially at an angle but something is catching\nno matter how I adjust the loose levers. It's been bouncing in my pack\nprotected by only a cloth draw-string bag.\n\nHave I screwed it up (pardon the pun)?