Does anyone know what type of thread st croix uses? It looks so translucent on some rods

I cannot speak to the type or brand of thread St. Croix uses on their rods, but I do know that in addition to darkening a couple shades, untreated nylon turns translucent when you don't use CP. I especially like that effect on my fly rods. Just be sure to use something to cover up any guide-foot dressing to avoid seeing a two-tone guide foot. You can use a black sharpie on a black guide foot to avoid the issue, but I'm not sure what you would use on some of the other guide colors (Titamium, gray, etc.)

Yes! I love the effect untreated nylon gives. It just seems like st croixs thread is SUPER translucent haha

I have spoken to St. Croix from time to time, and it seems that they simply use uncoated nylon thread that they finish with thread finish with no color Preserver.

I am not sure that a particular thread brand makes any difference at all with respect to the factors that you ask about.

However, for myself, unless specifically requested by a client, I will not use color preserver. I very much dislike the "artificial" look that is routinely created by the addition of this substance to a thread before applying finish.

To each his own.

St. Croix used Gudebrod in the past, but that is long out of production. I had the Gudebrod colors scoped out to a certain extent years ago, one of the higher end colors was a 4 digit special dye and not available to us, I have no idea what they use now. Probably have it still someplace if it's important to someone, hasn't been to me in a while.