[mkl]

An earlier article [1] linked in this one says about 1.2m radius, so ~2.4m or ~8ft diameter. At 48 seconds in the video there's a man standing next to the propped up side and it comes up to his chest, so that seems believable (the other side is down a slope).

It seems surprising it weighs 500kg though, as it's held up by a thin iron/steel pipe/bar. If it's solid mild steel at 7850kg/m^3, with an outer radius of 1.2m and inner radius of 1.05m, and a thickness of 4cm, that would be (π*1.2^2 - π*1.05^2)*.04*7850 ≈ 333kg. If the inner radius is 1.0m and thickness is 5cm, that would be ~543kg, so maybe it is that heavy.

Edit: The tooth profile looks strange for a gear. There's a clear but potato-resolution view at 36s in the video. The teeth have flat tops with sharp corners, the sides are pretty vertical, and the gaps have very rounded bottoms.

[1] https://nation.africa/kenya/counties/makueni/mystery-object-...