looks like silverline
A quick learner from norton mass says:
September 1, 2016
ordered parts for silverline that work looking for corner angles for repair
Paul from SWISCO responded:
September 6, 2016
Hello! I believe you have a 3/16" X 3/16" stamped corner key. We have one in that size in aluminum, our 95-176. Please compare this to what you have and let me know if it can work for you. It's important to measure your hardware, just in case.