Thanks for reaching out to us. The two pivot shoes you are showing look like our 15-046 which is used for the lower sash and the 15-154 pivot shoe which is usually used for the top sash with a indented front to compensate for the winged pivot bar. Have a look at the specifications and see how they compare with yours.
The weight you're referencing doesn't apply to the pivot shoes, but the spiral balance tube strength is determined by the window sash weight.
Sometimes the window tracks can be fickle, where the original 15-046 pivot shoe correctly works; then you replace it with a similar locking-style pivot shoe and it doesn't. You'd want to go with the 15-015 pivot shoe with a side brake instead of a back brake on the 15-046 and it works. So we recommend the 15-015 pivot shoe on this window, another window might work better with the 15-046 pivot shoe.
