The bulky bobbin does not fit on a regular flyer—you need the bulky flyer. The orifice of a bulky flyer will not fit into the bearing on a regular front maiden—you need the bulky front maiden for your Flatiron, Ladybug, Matchless, or Sidekick. You can use the whorls that came with your wheel on the regular flyer or the bulky flyer.
You need all three bulky parts: bobbin, flyer, and the front maiden for your wheel. However, if you own more than one of these Schacht wheels, you can purchase its front maiden separately.
The bulky flyer and bobbin cannot be used on the Schacht-Reeves wheel.