I have the HQ16 sit down and it will take any thread I have. I normally use 30, 40 or 50 wt cotton. I always sew out a test and adjust the tension. If you are only adjusting the top tension and it still doesn't look good your bobbin tension needs adjusting. The service tech here told me I'd probably have to adjust both tensions every time I change thread types and weights. I thought that was just crazy, I could not get my tensions to look good so I took it in for service. $160.00 later, turns out it was the bobbin tension, it was too tight. Next time I'm frustrated and have tension issues I'll go with the advice from the service tech. So sit back relax, drink your favorite beverage and keep trying.