Name for this type of connector?

[Mbira]

Anyone know what is the name for those spring-loaded button type things that are found on PA speaker stands (also keyboard stands) where the outer tube will have a hole in it and you slide the outer tube over the inner tube and that spring-loaded button pops through the hole on the outer tube to secure the stand at a certain height?  I'm trying to make something with that mechanism but I don't know what it's called...

 

[moamps]

http://www.rockwestcomposites.com/browse/tube-accessories/button-clips