Thought this might be helpful. I have a donut from a late model Crown Vic as a spare for my 1965 Barracuda. I chose this doughnut because of the 4 1/2 bolt pattern and that it does not protrude past the trunk floor.I needed a hold down to secure it and didn’t want to spend the money or wait for one on Ebay so I went to my Home Depot. I found this in the plumbing department. It turns out that it is held together with a 3/8 carriage bolt. It has a nice large wing nut and even a rubber washer that has a square cutout to fit the shank of the carriage bolt. It is the 3” model as there are different sizes. I bought a 5 inch carriage bolt and substituted it for the one that came with it. It cost less than $5.