Mezzo windows

Thanks for reaching out to us. Take a look at the 15-177 pivot shoe which is used with the Series 152 coil springs (sold separately). We don't have a 10-pound weight rating but you could use two S152-5 5-pound springs on each side of the window. That would be 10 pounds of support on each side for a total of 20 pounds of overall support for the window. For additional spring covers, see the 15-143, 15-144, and 15-145. These parts "sandwich" around each spring. 

Please let us know if you have any questions!