is the nut and saddle same matieral ?

is it possible to take the saddle and make it into a nut. i ask because i want to replace a damage nut on a old ukulele and i have a uncut piece of bone square that was originally to make a saddle. ive checked my other ukuleles and the nut seems to be a smooth plastic piece and the saddle appears to be bone.

As long as it's the proper dimensions! Doesn't matter what it was originally.

I've cut old guitar saddles to size as both ukulele saddles and ukulele knuts where the nut wasn't too chunky.
The parts I've re-used have always been bone. It's a lot harder to work / size than you might think. I cut to rough dimensions with as scrollsaw and finish to size on a coarse diamond whetstone. If you buy into polished bone sounds better, thats easier to acheive with increasingly fine abrasives, but leave yourself a little extra to polish, it always seems to wear a little quicker whe its close to size!

Short answer: yes. However, the nut has a far smaller effect on the sound than the saddle, so using a different material is fine.

It should be strong, but after that, anything you want to use. Many old ukes had wooden (rosewood or ebony) nuts, but I've seen other woods used.