If were looking for the length, or any other related how-to details, check out the excellent build summary thread by @steved:
If you are looking for some other dimensions of the metal struts, consider that the Fusion 360 model I made available has a 3d model of the metal strut inside it, and you can press hotkey “i” to get measurements on it.
Fusion 360 has a free hobbyist license so you can access the software for no charge.