I wonder if the vendor has a template to use to determine the type/size you need?
When I ordered a Tides Marine Strong track (a HDPE extrusion that slides into the mast slot), they sent me a package of “disks” with all sorts of track templates on it, so I could ID the exact size and dimensions of my mast slot so they could send me the right track. Worked great. Every thing fit perfectly,
Greg