Fishing line is all I use to serve strings.  I think this was 15 or 20 lb test. the spool wasn't marked any longer.  I just stuck the spool on a bobbin winder on a sewing machine to wind the line around it.

Why not use Halo?  Because mono is just as good in my opinion and that's what I have. Is mono better? probably not, but it's cheaper and, again, that's what I have.

I've used mono for years and have never had a serving break or come undone like some have expressed worry about.  It's tough stuff and lasts forever.  If you're in a situation where your serving gets nicked enough to cause it to break, you've probably cut your string..

Shove a stick or something where it fits tight inside the smaller spool.  Chuck the stick up in a drill and spin the mono of the big spool on to the smaller spool.  Wouldn't take but a second to do that.