Stems have 3 basic differences when it comes to interchangeability.
1. Threaded or threadless - threaded or quill stems are the stems that fit inside the steerer tube and have an expansion bolt. These are what old cruisers have. Threadless is what most new bikes have. These clamp over the steerer tube.
2. Steerer Tube Size - 1 inch, 1 1/8 inch, 1 1/4 inch, or tapered which is usually 1 1/8 at the top and 1 1/4 at the bottom.
3. Handle Bar Clamp Size - This is the size of the clamp where the bars go.
So you can use a BMX, MTB, Cruiser, Road, or any other stem as long as you know what what size you have. But to answer your question, yes, you can swap a 4 bolt clamp for a single bolt clamp.
