These are replacement runners for 17mm square curtain rails. They can be used with most household 17mm square curtain rails, but please be aware that they may not fit depending on the shape and size. To install, simply insert into the rail and rotate 90 degrees! Additional runners are available in sets of 8 for 200 yen. Please refer to the photos for the size. You can search for to see other items for sale. Please read my profile for information about transactions. Z2