Recommendations for underbrush cutting with a weedeater and brush blade...

I have a Stihl brushcutter Bought in 1986,still runs like a champ.Cuts 1/2”-1”” saplings like weed eater cuts grass.I even cut down 12” tree once,had my chainsaw pinched and only way to get it free.I actually haven’t used it much last few years,my stepson is using it this summer to clean up 3 acre lot that hs lot of junk saplings.

I found a Craftsman someone put on the street for the trash. It only runs at full throttle or off. Got a 2 pack of some circular saw looking blades on Amazon. It will cut down bigger stuff than what you're looking for. I would just loof for something used with a straight shaft.