I think if you got Straight Stitch Foot | Part Number: 200331009 that it may be very close to a quarter inch on either side. It looks like one of that part number has a second hole with out an opening which I don't understand - here are some for low shank machines without the guide.
https://www.amazon.com/DREAMSTITCH-2.../dp/B07DT1RVJV
https://www.sewingpartsonline.com/st...200125008.aspx (says will fit MC 6500 but only one hole)
https://www.sewingpartsonline.com/st...200331009.aspx
https://www.sewingmachinesplus.com/j-200331009.php
https://www.sewingpartsonline.com/1-...ow-p60801.aspx
https://www.amazon.com/Distinctive-Q.../dp/B0032654HI
Janey - Neat people never make the exciting discoveries I do.
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