About a year ago, I was the very fortunate recipient of a true barn find (actually, an old garage find.) The early '20s Runabout had been disassembled and stored fairly securely about 50 years ago, as nearly as we can determine. The old fellow that disassembled it, meant to get back to it, but never did. His son meant to get back to it, but died as soon as he retired and the widow, just wanted it, a Bugeye Sprite, a '50s Jag, and numerous other antiquities out of her life so she could move to Florida.
Now, these folks had carefully laid all the T parts together, boxed some and sorted various nuts, bolts, pins and rods into plastic bags. I thought I'd find everything I'd need to reassemble it, and had, until I came across the need to reattach the brake control shaft brackets to the frame rails. I found 2 hex head bolts of the right diameter, but only one of the correct length to fit the castle nut correctly snug. These bolts are more than 1/4 inch, and as nearly as we can measure, about 17/64ths. This is apparently a Henry one-off bolt size and is not shown in any parts catalog.
They were originaly 5/16".