If I had to guess, those could be the brushes that tractor came with when new!
No problem though, they sell repair kits with new brushes. They come with new bearings too so you can replace the bearing(s, depending on the end cap yours has).
Edit: looking at your pictures above I can see that you have the type with 2 bearings, some only have 1 bearing at the front and a bushing at the back.
You remind me that I really need to check the brushes on my 106, it's been working like a charm since before I bought it but who knows how worn they could be...
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'70 107 with k301 engine swap
'71 106 with 38" deck
'70 147
R with factory replacement k321, 42" deck
'61 Original with 38" timed deck
'63 70 "pinkie"
1863 with 54" deck
'46 Farmall H, '50 Farmall Cub
105 x2 (parts)