I bought one 164 yd skinny spool of mettler thread. can i use it on my horizontal thread holder or do i need to put it on the vertical one??

It depends on your machine. The machine I use most of the time has a vertical spool.

I use the mettler on the horizontal spool holder.

I recently purchased a new machine and when I went for my guide classes I had a traditional spool of Coats and Clark that I was practicing with on the vertical holder and the instructor told me that it belonged on the vertical holder and the skinny spools like mettler went on the horizontal holder.

My machine doesn't have a horizontal spool holder, but with the vertical spool it goes up to the guide and then comes back down to the first guide on the machine, so I don't need a horizontal one.

if thread is cross wound on the spool it can go on the horizontal spool. If wound straight then should go on the verticle holder. Bettler, Guterman, Sulky etc on the verticle spool, Coats, YLI etc on the horizontal.

Thanks for asking that question. Thank you Holice you taught me something new.

Thanks Holice. I knew there had to be a reason for the 2 different spool holders but when I bought the machine the saleslady just said it was an extra holder. Thanks!