Geez, do I feel like a dunce. I tried sewing some things up with heavy duty thread this weekend and just couldn't get it to work. The thread kept getting backed up in the needle.
I was using Coats & Clark heavy duty XP, with a 100/19 (I think, but not 100% on the second number) needle. I could look at going with a larger needle, but man it'd make a big hole. I was trying to sew some 4 oz cloth and it seemed like the 100/19 needle holes were huge. (In fairness, I sew with a 70 whatever most of the time, for momentum and silk and such.)
Is it simply a matter of going to a larger gauge needle? How big? And at what point do you reach for the heavy duty thread instead of the normal stuff?