standard nylon strings, medium tension. I would not advise to put anything else on it ;-)

@@theoldeuropeguitars 'great for slide playing' after putting on some steel strings

@@santrixhimself3679 if you want to destroy this historic instrument, go ahead! ;-)

@@theoldeuropeguitars no no, i wouldnt do that. Thats whst people would write in their ebay describtion;)

@Simon McCreath Some of them are playable, unless you expect a super low string action, then that is very rare. Sometimes you can sand down the bridge a bit (I did that on several occasions) to bring down the string action. In general, these were never intended to allow for singlenote speed runs on the higher up frets. They were supposed for mild chord strumming while singing folksy tunes at the campfire in the 1920s and 1930s, in the so called "Wandervogel"-Bewegung (wandering bird movement), a youth thing back then where juveniles went hiking and camping together, and sadly also exchanged a lot of not so nice ideas of the time. Anyway, especially when some were strung with steel strings, the neck (which does not have a truss rod) might be beyond repair.