A Continental product that I found to be a little bit disappointing. Which is a first for me to say about Continental products. It works. But not as well as almost all other Continental products. My main issue is that one of the valves in the stem does not like to allow air past it while pumping up. The other one works fine, without any problems. Another issue is that one of them, even though there is a seal where it threads into the tubes valve stem, it leaks unless you use pipe threading tape. Once these issues are overcome though they hold air. So they can work well if they don't have the same issues as one of the 2 in the package of 2 that I bought. So you might want to consider purchasing 2 of the 2 packs just in case. But you might get lucky. Because it's very possible that the one that I got that was a problem could just be an aberration. I honestly don't know, because I only bought one of the 2 packs. It's probably worth trying, because I believe that Continental productas are typically high quality.
Work perfectly on my Vittoria Corsa Elite tubulars. Unscrew the Vittoria valve with the provided tool, screw in the Conti extender, screw the Vittoria valve into the Conti extender. Done. No leaks.
I bought these extensions to enable me to mount some older Vitoria tubulars on some aero rims. Since they work by removing the core from your existing valve, installing the extension, and then reinstalling the core into the extension, you could add sealant to the tires without removing them from the rims if you needed to. Also, they are beefy enough to hold up to pumping by hand.
Unlike over the top extenders, the in line extenders enable you to accurately inflate your tires to the desired pressure. Additionally, if you ever need to use a foam sealant, the in line extender will yield better results. Make sure you tighten them properly to the tire stem using the provided tool and check for any leakage prior to mountinggluing your tubular tires.
I love these extenders. They are easy to install and they don't leak. I have used them over and over with different tires and I have even used tire sealent with them. You have to be careful putting them on that you don't turn too hard and ruin your tube or tire by twisting off the stem on the tube. Other than that they are great.