This tube endcap is made for telescopic tubes. The endcap needs a cut ring of vinyl tube placed in the "low area" to function. When assembled correctly, giving a twist to the interior tube of a telescopic tube set, will lock the tubes or unlock the tubes... adjusting the length.A similar function to this can be found in adjustable shower curtains.This tube endcap is made for telescopic tubes. The endcap needs a cut ring of vinyl tube placed in the "low area" to function. When assembled correctly, giving a twist to the interior tube of a telescopic tube set, will lock the tubes or unlock the tubes... adjusting the length.A similar function to this can be found in adjustable shower curtains.