will this lock work on a milgard sliding door handle that has a circle where the lock would be inserted?

Hello Bella, and thank you for your inquiry regarding this item from Prime-Line Products. It is very likely that this lock cylinder will work with your Milgard handle, as this lock fits handle sets used by a multitude of patio door manufacturers. For faster service, be sure to take advantage of the CHAT option located in the lower right-hand corner of your screen, where you can quickly be connected to a representative for assistance. Otherwise, you can contact the manufacturer directly with your questions regarding this item, or any other product manufactured by Prime-Line Products by calling their toll free number at (877) 649-9740, or by contacting them by email at prodtech@primeline.net