This are 10mm, 20mm, 30mm driveshaft extension for the scx24, if stretching out a deadbolt for say. Install the driveshaft extension onto your current front deadbolt driveshaft and install the c10/jeep links and now you have an easy extension without searching for a new driveshaft that are usually out of stock or unavailable for the stretch you're wanting. Buy the quantity you want and just install them together to get where you need to be. the female tube portion is designed to be appx the exact same length as the shortest scx24 male driveshaft portion which is used on most all of the scx24 models in the front. Will also work with rear longer male shaft but will not insert to flush.
To install just shove the male splined extension shaft into you current female shaft tube. Then reinstall. It will be very tight and you may need to slightly heat the driveshaft tube before installing the insert. It is designed to install and not come back out without breaking it. You can sand as needed. Or add more than 1 for longer wheelbases. each one adds 10mm length.
