Channel balance ID

I want to order 8 balancers for my windows. All the same balancer. I took the measurements as you directed, see the attached photos. From this and following along on you web site I believe the balancer I need is the 29 inch 380. My window weighs 20 lbs. I'm not sure of the specific balancer needed for this window. Can you help me? I need a top sash and it appears the Howmet is the one but it has just one screw while my window has two. Please check the photos. Can you help? I have followed your videos which were very helpful. Can you guide me and help me order the necessary balancers? Please call me. The stamped marking on the balancer is 28C