Double knitting sport or worstead

i design and sell baby patterns, i translate them into usa terms, i have been to the usa quite a few times, last year i bought a lot of different yarn to try to tell my usa buyer what to buy when making my patterns, i have made all the swatches and have been measuring rows and stitches, i usually say use sport or knitting worstead, anyway bernat satin says its worstead and is nearest the guage i need it is worsted, red heart soft yarn says it worstead but it much thicker, sport is pretty close, any suggestions, or do i still say sport/worstead

If I understand you correctly, in the sampling you did when you used the Red Heart yarn even though it had printed on the label worsted it was probably a medium worsted instead of a light worsted (dk). I have found that when using sports or light worsted (dk) yarn with the same needle size I sometimes get a smaller gauge with the sports yarn. If I were knitting up a baby pattern like you are I would specify either sport or light worsted (dk), with a possible lean towards sport if selling in the US. This web site might also be helpful to you: http://www.yarnstandards.com/weight.html

HTH.
Katrina

thank you for that it get quite confusing as sometimes usa yarn has numbers aswell, less complicated in uk i think

I think it has to do with what someone is more familiar with, that way when you picture the type or weight in your mind a picture of what you can make from that yarn pops up. I know I still get confused with needle sizes since in the UK millimeters are used versus the numbering system that is applied in the US.
Katrina

what?