Remnants after boole cut is made.

 From:  Michael Gibson
3217.2 In reply to 3217.1 
Hi Leonard, when you see things like that it usually means that there is a bad configuration of trim curves on the resulting object.

Something like the trim curves are self-intersecting (crossing one another) rather than having a clean arrangement.

Your object is probably getting to be of a little bit too small scale here, I notice that some of the pieces are a little wiggly - this is likely happening because you are approaching too closely to the default 0.001 fitting tolerance.

Also normally it is actually not a very good idea to model individual screws that are going to be part of a larger object.... It just adds such a tremendous amount of weight to your model it is usually better to make threads with a texture map in your rendering program rather than trying to actually model the threads individually, especially if there will be many of them.

I'll see if I can find out anything else by taking a closer look at your objects.

- Michael