I just installed a 3 section, 30' Channel Master telescoping mast that I had lying around my warehouse for neary a decade. I'm going to need every foot of its length.

It didn't occur to me until I had mounted it, but I don't know if there is any kind of positive stop on the extensions, or if I risk pushing a section completely out of the one below it.

I don't feel like taking this mast down to analyze it. Does anyone know if there is something to prevent the sections from being deparated? If not, then I'll have to bring a stiff tape measure with me and take some measurements when it is most of the way extended. How much overlap should I leave?

I put this mast up about a year ago and, as best as I can recollect, there was some type of stop that prevented the extensions from pushing beyond each section. The reason I recollect this is that I was only going to use 20' of it at first and I remember having to push the top most section back through to the bottom of the mast to remove it. Hope this helps.