Differential Pulley for the Yokomo YR-4 II. This is better resin printed with ABS like resin as it is fairly intricate and as I found out, removing support from it on an FDM printer tends to take small edges off with it.The one in the photo is printed from ASA but this may wear quickly with the belt friction. If you want to FDM print it Polycarbonate may be better although this can have issues with the grip on the belt.Should be a direct fit replacement part.

Use the 'Convert to polyholes' setting on Orca slicer for best results replicating the holes accurately.