That's what spool caps are for. My Pfaff 2170 came with 2 sizes, even the Imagine serger had them. If your machine is set up for cone thread, you might not get any but can probably find some to fit the spool holder.
Here's a picture of some:
http://www.sew4less.com/category/51/..._and_Spool_Pin
You might have a dealer closer that you can purchase from.