Hi,
Up for sale are stem extenders.
The first number is the thread of your existing stem. The second is the thread of your crown.
For example you have a threaded stem .9 and want to put a crown made for a .7, with this you can!
Price is for 1 stem extender. Although I also have .7 and .9 as bundles of 10.
Don't hesitate if you have questions.