Mine has two different 'collets'. One for larger bits, and the other for smaller bits. Here's a couple of things to check:
- twist the end off of the pinvise so that the 'collet' comes out. Pull it out and see if there's another end on it. If so, it likely has a smaller end on it that is used for smaller bits. Reverse it in the pin-vise, reassemble the end, and you should be off.
- I have another pin-vise where the extra 'collet' is stored in the handle. Check to see if the back of the handle twists off and whether or not there is another collet stored in there. If so, it's likely the one that goes to a smaller size.
Good luck!!
Murray