There are several reasons to use a stem extender. If you still have your original stem but it is broken and too short to use with your crown, you can buy a stem extender to lengthen the original broken watch stem to extend to the correct length that you need for your repair. If you have a pocket watch that has broken off and there is not a pocket watch stem available in a replacement, you can use a watch stem extender to lengthen the stem to fit into a pocket watch. If you need to change the thread size of a stem you can use an extender that will change the thread (tap) size from a larger or smaller size to a standard thread (tap) size. You can also find replacement extenders that will change a regular stem into a male or female stem to fit a one piece case. Here you can select the perfect watch stem extender for your specific watch as they are sold individually. Simply select the Tap size you need to lengthen, or the tap size you want to change your original stem to, or the male or female end that you want to change your stem into. Simply choose the stem that you would like from the drop down menu above.