MK 1 Grand Cru 50.4bcd crankset, bare arms
These MK 1 crank arms come without chainrings or chainring hardware, so you can assemble your own custom gearing. Get singlespeed hardware and singlespeed rings, or double hardware and a big ring and small ring.
Note: when you use these cranks with a singlespeed ring, the narrowest bottom bracket you can use is a 116mm, but that will only work on bikes with narrow chainstays such as road racing or track bikes. (43mm chainline with a 116mm bb.)