I have a 3-arm crank (101mm BCD I believe). It has 2 steel chainrings that are riveted together and these chainrings are the common setup. Simplex made an adaptor so you can screw together 2, 6-hole patterned chainrings for "custom" setups (see picture below). This adapter is for a 157mm BCD chainring. I have seen 46 teeth chainrings that will fit on this but is there anything smaller? I've seen smaller TA 6-hole rings but I just found out they are a 152mm BCD.