what is this called

Hello,

The part indicated in your photos is called glazing bead, which holds the glass inside the sash frame. We carry a large selection of replacements, which you can view here. To determine if we carry a match for yours, we would need to see an end profile photo of your glazing bead uninstalled. Take a look at the videos related on this page to assist you. 

Also, please note that our replacement options are fairly rigid, meaning that they would only work for the sides and the bottom of your windows. The arched top would be too curved to install one of our parts. We apologize for the inconvenience.