First, you want a tillering string that's as short as possible. So if you're making up different length bows then you might want to make up several different length tillering strings. Personally, I like the double loop tillering strings. Mostly I use old 12-14 strand double loop bow strings for tillering strings. I do have a 16 strand double loop tillering string made up for longer bows. I'm probably not pulling more than 35-40# with my tillering strings (up to or just past what would be my normal brace height on the tillering board) before I go to my permanent string. Hope that helps.
ART B